IK  ME/ 

John 

^©MAM 
Swett 

GEOLOGICAL 


OR, 


THE  RUDIMENTS  OF  GEOLOGY 


FOR  YOUNG  LEARNERS. 


BY  ALEXANDER  WINCHELL,  LL.D., 

PROFESSOR  OF   GEOLOGY  AND  PALAEONTOLOGY  IN  THE   UNIVERSITY  OF  MICHIGAN. 
FORMERLY   DIRECTOR    OF    THE   GEOLOGICAL    SURVEY    OF    MICHIGAN. 
AUTHOR  OF  "SKETCHES  OF  CREATION,1'  "WORLD  LIFE," 
ETC..   ETC. 


Science-teaching  should  begin  early  in  the  school-course. — 

PRESIDENT  ELIOT,  Harvard  University. 


CHICAGO: 

S.  C.  GRIGGS    AND    COMPANY. 

1884. 


COPYRIGHT,  1884, 

BY  8.  C.  GRIGGS  AND  COMPANY. 
i|Oh    D 


E^Hf^yaaaj 


CONTENTS. 


PAOB 

PREFATORY  NOTE I 

A  WORD  WITH  THE  TEACHER 5 

i 
SOME  PRACTICAL  SUGGESTIONS 

STANDARD  SAMPLES  OF  MINERALS  AND  ROCKS      ...       11 

EXCURSION  I.— In  the  Garden. 

ORGANIC  AND  INORGANIC       .  13 

EXCURSION  II.— In  the  Garden  and  Field. 

BOULDERS  AND  SAND 15 

EXCURSION  III.— To  the  Gravel  Bank. 

THE  DRIFT 21 

EXCURSION  IV.— To  Another  Gravel  Bank. 

SPRINGS  AND  WELLS 26 

EXCURSION  V.— To  Our  Laboratory. 

How  THINGS  ARE  PUT  TOGETHER 30 

EXCURSION  VI.—  To  the  Field. 

QUARTZ 36 

iii 

f>4  \  V  I  0 


iv  CONTENTS. 

EXCURSION  VII.— To  the  Field. 

THE  FELDSPARS 40 

EXCURSION  VIIL— To  the  Field. 

CALCITE 46 

EXCURSION  IX.— To  the  Field. 

THE  MICAS,  HORNBLENDE  AND  TALC 50 

EXCURSION  X.— Among  the  Boulders. 

QUARTZOSE  ROCKS 54 

EXCURSION  XI.— Among  the  Boulders. 

MICACEOUS  ROCKS 57 

EXCURSION  XII.—  With  the  Stone  Cutter. 

HORNBLENDIC    ROCKS 62 

EXCURSION  XIIL—  To  the  Marble  Yard. 

CALCAREOUS  ROCKS 69 

EXCURSION  XIV.— To  the  Clay  Pit  and  the  Field. 

ARGILLACEOUS  ROCKS 74 

EXCURSION  XV.—  To  the  Specimen  Drawers. 

EXERCISES  IN  IDENTIFICATIONS 78 

EXCURSION  XVI.— By  the  Waterside. 

SEDIMENTS 81 

EXCURSION  XVII.— In  the  Gorge. 

DECAY  AND  EROSION  OF  ROCKS      ......       87 


CONTENTS.  V 

EXCURSION  XVIII.—  At  the  Rocky  Ledge. 

STRATA  AND  SYSTEMS  OF  STRATA    .  95 

EXCURSION  XIX.— To  the  Diagrams. 

How  THE  STRATA  ENWRAP  THE  EARTH    ....     101 

EXCURSION  XX.  —  To  the  Geological  Map. 

How  TO  UNDERSTAND  A  GEOLOGICAL  MAP     .      .      .     109 

EXCURSION  XXL— To  the  Geological  Map. 

GEOLOGICAL  SECTIONS       .........     116 

EXCURSION  XXIL— To  the  White  Mountains. 

THE  Eozoic  ROCKS     .  123 

EXCURSION  XXIII.—  To  the  Upper  Mississippi. 

CAMBRIAN  (OR  LOWER  SILURIAN)  ROCKS  AND  HISTORY     131 

EXCURSION  XXIV.—  To  Niagara  Falls. 

SILURIAN  ROCKS  AND  HISTORY 140 

EXCURSION  XXV.—  To  Mackinac. 

DEVONIAN  ROCKS 146 

EXCURSION  XXVI.—  To  Burlington,  Iowa. 

THE  LOWER  CARBONIFEROUS  ROCKS 153 

EXCURSION  XXVII.—  To  the  Coal  Mines. 

THE  COAL  MEASURES 160 

EXCURSION  XXVIII.—  To  Selma,  Alabama. 

THE  MESOZOIC  ROCKS       .  168 


CONTENTS. 


EXCURSION  XXIX.—  To  Claiborne,  Alabama. 

THE  TERTIARY  FORMATIONS 173 

EXCURSION  XXX.— To  the  ftiver  Valley. 

QUATERNARY  FORMATIONS 178 

EXCURSION  XXXI.—  To  Switzerland. 

ABOUT  GLACIERS 185 

EXCURSION  XXXII.—  Through  the  Ages. 

ABOUT  THE  PLANTS  AND  ANIMALS  OP  THE  PAST      .     191 

QUESTIONS  ON  THE  TEXT 202 


PREFATORY  NOTE. 


ADDRESSED  TO  TEACHERS  AND  SCHOOL  OFFICERS. 

r  I  lHAT  the  elements  of  geology  are  so  seldom  taught  either  in 
-L.  our  primary  or  secondary  schools  is  a  circumstance  to  be 
regretted.  No  tendency  seems  manifest  toward  any  improvement 
in  this  particular.  In  Michigan,  which  enjoys  a  justly  high  repu- 
tation for  the  excellence  of  its  schools  and  teaching,  even  less 
geology  is  studied  in  school  than  was  customary  a  dozen  years 
ago.  No  knowledge  whatever  of  this  subject  is  required  for 
entrance  into  the  University  of  Michigan  in  the  "  Classical 
Course,"  nor  in  the  "  Scientific  Course,"  nor  in  the  so-called 
"  English  Course  " — though  in  the  last  two  courses  the  candidate 
is  given  his  option  between  preparation  in  Chemistry,  Geology, 
Zoo'logy  and  Physiology.  Of  necessity,  Physiology,  which  is 
generally  taught  in  the  schools,  is  almost  always  the  chosen  sub- 
ject, though  next  to  this  stands  Chemistry.  Practically,  there- 
fore, the  study  of  geology  in  the  University  begins  with  the 
elements  in  every  course.  A  similar  state  of  things  exists  in 
most  of  our  colleges.  There  is  no  course  where  geology  is  a 
prerequisite,  so  that  the  student  on  entering  may  find  himself  in 
position  to  push  on  to  some  advanced  knowledge  of  the  subject. 
One  would  anticipate  that  a  course  specifically  denominated 
"  Scientific,"  would  demand  a  more  extended  scientific  prepara- 
tion than  the  old  "  Classical "  course,  and  that  a  science  which 
has  done  as  much  for  industry,  civilization  and  culture  as  geology 
has,  would  not  fail  to  be  enumerated  among  the  requirements. 

Since  geology  is  not  so  required  for  entrance  into  college,  it 
has  ceased  to  be  taught  in  the  schools — as  if  geology  had  no 

i 


%  PKEFATORY   NOTE. 

uses  if  not  demanded  as  a  preparation  for  college.  This  seems 
to  the  present  writer  a  greater  mistake  than  the  other.  For 
assuredly,  the  large  majority  of  pupils,  not  expecting  the  oppor- 
tunity for  collegiate  study  of  the  science,  have  reason  to  com- 
plain that  they  must  be  deprived  altogether  of  the  opportunity 
to  learn  even  the  nature  of  the  subject.  When  they  enter  upon 
the  affairs  of  adult  life,  and  especially,  if  they  mingle  in  the 
intellectual  life  of  the  age,  they  find  living  questions  agitating 
the  world,  before  which  they  must  remain  dumb  and  uninformed, 
because  their  merits  are  rooted  in  the  great  facts  of  the  earth's 
history  and  the  history  of  life. 

Such  life-long  ignorance  of  geology  is  quite  as  unnecessary  as 
deplorable.  The  elements  of  the  science  are  not  a  body  of 
principles  difficult  to  master,  nor  encumbered  with  a  greater 
number  of  scientific  terms  than  the  sciences  of  physiology, 
chemistry  and  botany.  The  data  of  geology,  moreover,  lie  all 
about  us,  and  are  the  most  obtrusive  and  noticeable  of  all  the 
objects  which  we  daily  encounter.  Stones  and  rocks  never  fail 
to  awaken  the  curiosity  of  the  boy  or  girl;  and  there  are  few 
children  who  have  not  made  collections  of  stones,  distinguishing 
their  varieties  by  precisely  the  same  characters  as  the  most  expert 
student.  Assuredly,  it  seems  a  dictate  of  educational  philosophy 
to  take  a  hint  from  these  childish  predispositions  and  aptitudes, 
and  shape  the  child's  education  with  some  regard  to  what  he 
seems  peculiarly  fitted  to  study. 

But,  however  appropriate  and  useful  this  study,  where  are  the 
teachers  who  will  properly  lead  the  pupil?  They  are  exceedingly 
few  in  number.  As  geology  is  not  taught  in  the  schools,  and  as 
nineteen-twentieths  of  our  teachers  have  not  studied  it  in  college, 
there  is  almost  no  preparation  among  the  teachers  of  primary 
and  secondary  grades  to  induct  a  pupil  into  an  elementary  knowl- 
edge of  the  subject.  In  this  state  of  the  case,  it  would  seem 
very  difficult  to  begin  the  desired  improvement. 

To  the  writer,  the  only  hope  of  early  reform  seems  to  lie  in 
furnishing  teachers  with  a  text  book  so  framed  as  to  be  capable 


PREFATORY   NOTE.  3 

of  successful  use  by  a  teacher  without  previous  acquaintance 
with  the  subject.  Certainly,  no  such  text  books  exist;  for, 
though  there  are  several  which  might  be  employed  by  teachers 
thoroughly  disciplined  by  previous  study,  the  large  majority  of 
our  teachers  are  not  so  disciplined,  and  it  may  not  be  necessary; 
and  these  text  books,  moreover,  are  too  much  conformed  to  the 
dogmatic  or  didactic  method  —  telling  about  things  which  are  far 
away,  or,  if  near  at  hand,  are  not  identifiable  by  the  aid  of  the 
book.  Due  discrimination  is  not  observed  between  those  concep- 
tions of  the  subject  which  are  abstract  and  beyond  the  reach  of 
the  young  pupil,  or  older  novice,  and  those  which  can  be  attained 
through  accessible  concrete  illustrations.  Many  of  them  are 
good  systematic  presentations  of  the  subject,  but  they  are  pro- 
nounced "dry"  and  unintelligible.  They  are,  in  truth,  too  sys- 
tematic and  too  complete. 

The  present  author  has  pursued  a  fundamentally  different 
plan,  and  hopes  he  has  prepared  a  primer  of  geology  so  simple 
and  so  intelligible  that  no  previous  preparation  of  the  teacher 
will  be  needed.  Hence  any  teacher  who  will  pursue  the  method 
will  obtain  an  insight  into  the  subject,  and  will  be  able,  also,  to 
lead  pupils  of  very  tender  years.  One  lesson  which  the  author 
has  learned  from  much  experience  is  here  applied.  The  beginner, 
especially  if  young,  retains,  as  the  result  of  his  first  course  of 
study  in  any  subject,  a  surprisingly  small  amount  of  tangible  and 
available  information.  This  is  the  author's  first  principle  of  pro- 
cedure. His  second  is,  to  enlist  the  senses  and  the  sentiments. 
Hence  the  method  is  essentially  inductive;  the  book  speaks  to 
the  pupil  in  the  second  person ;  it  leads  to  the  application  of  each 
item  of  knowledge  in  some  useful  or  interesting  relation,  and 
seeks  to  awaken  the  thought  of  the  learner. 

More  specifically,  it  directs  a  large  amount  of  attention  to  the 
pebbles  and  stones  so  abundant  everywhere  in  the  drift  of  the 
northern  states;  and  to  the  phenomena  of  sedimentation  and 
erosion  everywhere  accessible.  From  these  most  familiar  illus- 
trations, it  passes  to  the  phenomena  of  stratified  rocks  and  the 


4  PREFATORY   NOTE. 

way  they  are  arranged  upon  the  earth.  Here  much  use  is  made 
of  maps  and  sections,  as  these  train  the  learner  to  the  indispen- 
sable conceptions  of  superposition,  succession,  continuity  and 
discontinuity.  Not  much  is  said  about  purely  systematic  geology, 
and  still  less  about  palaeontology  and  geological  theory.  These 
divisions  of  the  subject  are  more  abstract  and  complicated,  and 
ought  to  be  deferred  till  some  familiarity  is  acquired  with  the 
conceptions  capable  of  illustration  from  familiar  facts  and 
phenomena.  Then  much  stress  is  laid  upon  the  "  Exercises." 
These  are  not  mere  questions  on  the  text.  The  answers  to  many 
of  the  questions  are  only  inferences  from  statements  in  the  text. 
Some  are  practical  applications.  Frequently  the  question  leads 
to  an  extension  of  knowledge.  Some  questions  are  asked  which 
will  require  considerable  reflection  —  some  even,  which  cannot  be 
answered  categorically.  It  is  intended  that  the  pupil  shall  keep 
the  question  in  mind,  and  search  for  the  proper  answer  by  asking 
his  elders,  by  consulting  books  or  by  exploring  in  collections  of 
specimens.  It  is  profitable  to  have  something  to  ponder  over. 

There  is  not  a  great  amount  of  science  imparted.  It  is  sur- 
prising—  often  discouraging,  to  observe  how  limited  is  the  total 
amount  of  exact  knowledge  acquired  even  by  older  students  after 
a  more  thorough  course.  It  is  also  an  interesting  fact  that  a 
very  little  knowledge,  if  it  is  fundamental,  and  fully  mastered  by 
viewing  it  from  all  sides,  will  serve  to  answer  a  very  large  number 
of  common  inquiries.  It  is  also  true  that  a  good  deal  of  verbiage 
is  employed.  Many  sentences  add  nothing  to  the  statement  of 
facts.  They  are  intended  simply  to  control  attention  and  keep 
alive  the  pupil's  interest. 

The  very  gist  of  the  method  is,  that  the  pupil  shall  do  all  that 
is  indicated,  and  positively  see  every  thing  that  is  described,  as 
far  as  possible.  Great  efforts  must  be  made  to  render  this  pos- 
sible. Just  so  far  as  anything  must  be  studied  about,  without 
the  opportunity  to  handle  and  examine  it,  and  make  drawings  of 
it,  so  far  the  pupil  is  unfortunate;  so  far  the  plan  of  the  book  is 
not  brought  into  practice. 


A    WORD    WITH   THE   TEACHER.  5 

A  large  part  of  these  "  Excursions  "  has  been  used  in  actual 
trials  by  actual  teachers,  while  yet  in  manuscript.  The  result 
encourages  the  hope  that  they  may  be  found  suited  to  the  object 
set  forth,  and  may  thus  become  instrumental  in  diffusing  knowl- 
edge and  appreciation  of  a  branch  of  science  as  accessible  as  any, 
and  as  fruitful  as  any  in  results  of  high  value  in  the  industries 
and  culture  of  modern  civilization. 

This  primer  is,  therefore,  commended  to  the  candid  considera- 
tion of  teachers  and  school  officers,  in  the  hope  that  they  already 
feel  the  desirability  of  early  instruction  in  geology,  and  may  be 
disposed  to  join  with  the  author  in  testing  the  value  of  the  method 
which  is  here  proposed. 


A  WORD  WITH  THE  TEACHER. 

Here,  ladies,  is  a  little  book  in  which  I  hope  you  will  be 
interested.  I  address  you,  because  nearly  all  the  teachers  of 
those  for  whom  the  book  is  suitable  are  women;  and  also  because 
I  have  found  women  especially  interested  and  apt  in  the  studies 
which  are  here  introduced.  The  book  is  thought  to  be  so  simple 
that  it  will  literally  "  teach  of  itself,"  if  you  let  it  have  its  way. 
So  you  need  not  be  deterred  from  forming  a  little  class  in 
"geology"  in  consequence  of  having  geology  omitted  from  your 
own  education.  It  is,  I  confess,  too  childish  in  style  for  your 
own  use  as  a  learner ;  but  please  consider  that  you  are  not  the 
pupil  —  only  so  far  as  you  may  find  it  desirable  to  become  a 
pupil. 

Now,  please  permit  me  to  note  concisely  what  seem  to  me 
the  points  most  essential  in  making  this  little  book  a  success  : 

1.  Positively  do  and  have  done  everything  indicated  in  the 
text.  Do  not  say  some  of  these  things  are  so  simple  or  so 
obvious  that  the  doing  would  be  a  mere  form.  Probably  some- 
thing will  turn  up  which  you  or  your  pupils  could  not  anticipate. 


6  A   WORD   WITH   THE   TEACHER. 

Do  not  be  afraid  to  take  hammers  and  collecting  bags  or  baskets 
into  the  garden  or  the  field,  and  actually  break  the  rocks  and 
study  them  and  bring  them  home.  No  matter  about  keeping 
quiet  in  this  class.  The  very  study  requires  talking  and  move- 
ment. The  novelty  of  the  method  and  its  conformity  with  the 
impulses  and  instincts  of  the  child's  nature  will  assuredly  make 
it  the  favorite  class  of  the  school. 

2.  Should  you  happen  to  be  located  in  a  large  city  or  upon 
a  prairie  or  other  section  of  the  country  where  boulders  are  not 
easily  accessible,  the  best  recourse  will  be  to  a  wagon  load  or 
two  of  boulders  brought  from  some  boulder  region  and  thrown 
down  in  the  school  yard.     These  may  be  broken  into  moderate- 
sized  fragments  by  any  man  with  a  large-sized  stone  hammer. 
All  teachers,  as  a  provision  against   rainy  days,  might   have  a 
large  lot  of  fragments  placed  under  a  shed.     Even  teachers  in 
states    south    of    the    boulder-covered    regions    of    our    country 
might  get  a  supply  by  the   cheap   help  of   a  freight   car  from 
the  North. 

3.  A  day  or  two  before  the  class  is  taken  on  an  "  Excursion," 
read   it   over  yourself  so   as  to   know  what   to   expect,   and   be 
prepared   for  its  requirements.     When   the  excursion  is  taken, 
you  may  let  every  pupil  carry  a  book;  or  if  you  think  better, 
only  carry  one  yourself,   and    read    aloud    from    it,   giving   the 
pupils  time  to  examine  and  think  and  respond. 

4.  Make  yourself  sure   that   every  pupil  sees  and  does  and 
understands  everything  which  is  required,  and  does  the  best  he 
can  in  answering  all  questions.     Be  deliberate  enough  to  render 
this  possible.     Sometimes   the  lesson  will   need  to   be   divided. 
With   some   classes   it   will   be    best   to   devote   an   hour  to  the 
excursion  proper,   and   then  the   "  Exercises "  may   occupy  the 
time  on  the  next  day.     This  may  be  the  best  method  with  all 
classes.     Sometimes   the   whole   must   be   twice  gone   over.     In 
almost   every  lesson   the   positions   of    localities  mentioned  will 
have  to  be  studied  from  the  School  Atlas. 

5.  Accustom  yourself  and  your  pupils  to  copying  the  figures 


A   WORD    WITH   THE   TEACHER.  7 

in  the  book;  and  practise  still  more  in  making  drawings  of 
other  things  not  figured,  such  as  gravel  banks,  boulders,  cliffs, 
ravines,  landscapes.  Do  not  say,  "  I  never  took  a  lesson  in 
drawing,"  for  the  most  finished  draughtsmen  were  once  in  the 
same  situation.  Try.  Try  again,  and  so  continue.  If  you  are 
already  somewhat  practised  in  drawing,  you  will  find  your  skill 
extremely  useful.  The  geological  sections  required,  and  the 
other  exercises  on  the  geological  map  may  be  troublesome  at 
first,  but  no  exercises  can  be  more  profitable. 

6.  Lay  much  stress  on  the  "Exercises"  and  invent  addi- 
tional ones.  Some  of  them  are  merely  intended  to  set  pupil 
and  teacher  to  thinking  and  investigating.  Some  of  the  ques- 
tions cannot  be  definitely  answered.  When  a  question  is  pro- 
posed which  you  cannot  answer  at  once,  say  so  frankly.  We 
all  have  to  confess  ignorance.  I  think  the  "  Exercises "  will 
awaken  much  interest.  You  will,  of  course,  have  to  ask  many 
questions  on  the  text  and  its  subject  matter;  but  these  you  will 
frame  for  yourself  or  find  at  the  end  of  the  book. 

?.  Adhere  strictly  to  the  method  indicated  in  the  book; 
but  vary  the  details  according  to  the  circumstances,  and  extend 
the  instruction  and  the  observations  according  to  your  own 
judgment. 

8.  Have  every  pupil  collect,  preserve  and  label  specimens. 
A  good  plan  to  pursue  is  the  following:  To  each  specimen 
attach  a  little  circular  bit  of  white  paper  to  receive  the  "  school 
number."  Let  each  different  species  or  variety  of  minerals  and 
rocks  receive  a  separate  number.  Those  which  are  the  same 
species  or  variety  will  receive  the  same  number.  In  a  little 
book  write  the  numbers,  and  the  names  of  the  specimens  cor- 
responding to  them.  Let  each  pupil  also  attach  to  each  of  his 
own  specimens,  a  little  colored  paper — each  pupil  choosing 
some  different  bright  color;  or,  if  the  same  color  as  that  of 
another  pupil,  let  it  be  cut  oval  or  square  or  diamond  shaped; 
so  that  each  pupil's  specimens  can  be  picked  out  when  all  are 
placed  in  a  pile  together.  Have  each  pupil  also  keep  a  cata- 


8  A    WORD    WITH   THE   TEACHER. 

logue.  Then  the  number  on  the  white  ticket  stuck  to  each  of 
his  specimens  will  give  the  name  of  the  specimen  as  soon  as 
he  refers  to  his  list.  You  will  find,  a  little  beyond,  some 
practical  directions  for  this  work. 

9.  Use  other  specimens  additional  to  those  collected  by  the 
class  if  it  is  possible  to  do  so.  By  this  means  you  will  get 
for  study  more  species  and  varieties.  There  may  be  some 
small,  neglected  collections  or  single  specimens  in  your  neigh- 
borhood, lying  on  dusty  mantels,  what-nots  and  etageres.  Look 
them  up  and  press  them  into  service.  I  am  sure  you  will  find 
many  sorts  which  are  not  mentioned  in  this  little  book,  because 
the  book  mentions  the  most  common  things,  which  it  is  most 
important  to  know  something  about;  while  people  generally 
seek  to  lay  up  rare  things  from  distant  regions.  But  use  all 
that  you  can.  Besides  this,  there  ought  to  be  a  small  labelled 
collection  obtained  from  some  reliable  dealer,  furnishing  true 
examples  of  the  more  common  minerals  and  rocks.  Such  a 
collection  can  be  purchased  for  two  or  three  dollars,  or  a 
better  one  for  five  dollars. 

All  that  may  be  learned  by  the  aid  of  this  little  book  will 
only  conduct  the  pupil  over  the  threshold  of  the  subject.  But 
even  so  much  may  be  made  highly  interesting  and  indeed  very 
useful.  Beyond  this  threshold  are  departments  of  the  subject 
not  mentioned  here,  and  a  whole  range  of  ideas  and  conclusions 
about  the  history  of  the  world,  and  of  other  worlds,  which  would 
not  be  appropriate  here,  but  which,  nevertheless,  are  extremely 
fascinating  to  the  student,  and  tend  greatly  to  enlarge  and 
ennoble  his  intelligence. 

Now,  I  wish  to  feel  in  communication  with  all  the  teachers 
who  try  to  use  this  primer.  Please  exercise  the  freedom  to 
write  on  any  point  which  you  think  may  require  further  eluci- 
dation from  the  author. 

ALEXANDER  WINCHELL. 

UNIVERSITY  OF  MICHIGAN, 
ANN  ARBOR. 


SOME  PRACTICAL  SUGGESTIONS. 


FOR  STUDENTS  OF  ALL  GRADES. 

1.  Hammers    and    some    other    instruments    best    suited   for 
breaking  and   studying  rocks  are   described   in    Excursions  VI 
and  VII. 

2.  For  making  the  little  circular  or  oval   tickets,  white  or 
colored,  a  saddler's  or  tinner's  "  punch  "  is  suitable.     One  which 
will  cut  tickets  three-sixteenths  of  an  inch  in  diameter  is  large 
enough  for  small  specimens.     If  many  tickets  stick  together  as 
they  come  from  the  punch,  place  a  lot  in  one  hand  and  rub  them 
with  the  fingers  of  the   other  hand.     Fold  the   paper  so  as  to 
punch  through   several  thicknesses  at  each   blow.      Use  a  thin 
quality  of  paper. 

3.  For  attaching  the  tickets  do  not   use   common  mucilage, 
but  prepare  a  cement  as  follows: 

Clear  Gum  Arabic, 2    oz. 

Fine  Starch, H  oz. 

White  Sugar, I  oz. 

Rub  them  together  in  a  mortar;  add  as  much  water  as  the  laun- 
dress would  use  for  that  amount  of  starch,  and  wait  till  the  gum 
arabic  is  well  dissolved;  then  cook  the  solution  in  a  vessel  sus- 
pended in  boiling  water  until  the  starch  becomes  clear.  The 
cement  must  be  nearly  as  thick  as  tar.  Keep  it  in  a  wide- 
mouthed  bottle  stoppered  by  a  cork  having  a  small  round  bristle 
brush  passing  through  it.  Drop  in  a  small  lump  of  gum  camphor 
to  prevent  souring  and  mouldiness.  It  will  keep  a  year  or  more. 
When  too  much  dried  away  add  a  little  water.  This  cement  is 
strong,  and  is  good  for  repairing  breakages  of  specimens,  and 
also  for  attaching  specimens  to  cards  for  exhibition. 


10  SOME    PRACTICAL   SUGGESTIONS. 

4.  When  many  specimens  are  to  be  ticketed  at  once,  spread 
them  on  a  table  and  touch  each  one  in  a  proper  place  with  the 
tip  of   the  brush,  leaving  a  little   cement,  but  not  too  much. 
Spread  a  quantity  of  well  separated  tickets  on  the  table;  moisten 
the  tip  of  your  finger  on  the  tongue  or  a  damp  towel,  and  pick  up 
a  ticket  and  press  it  firmly  on  one  of  the  gummed  spots;  then, 
as  some  of  the  cement  probably  adheres  to  your  finger,  remove 
it  on  your  tongue  or  the  damp  towel,  and  pick  up  another  ticket 
and  attach  it  in  the   same  way.     This  method  is  rapid.     After 
a  half  hour  the  tickets  will  be  dry  enough  to  receive  the  num- 
bers.    Use  only  the  blackest  and  best  ink  in  writing  them,  with 
a  fine-pointed  steel  pen,  and  make  the  figures  perfect  as  possible. 

5.  Good  cabinet  rock  specimens  are  generally  dressed  to  a 
rectangular  shape  if  possible.     For  a  school  cabinet  they  may  be 
about  two  and  a  quarter  by  three  inches  square,  and  one  or  two 
inches  thick.     But  it  is  better  to  have  a  shapeless  specimen  than 
none  at   all.     Most  of   the  pupils  will  probably  be  suited  with 
mere  fragments.     But  in  all  cases,  some  approach  may  be  made 
to   the   standard   form.     Mere    minerals   must    be    preserved   as 
we  can  get  them.     When  a  specimen  is  reduced  nearly  to  the 
requisite  size,  the  trimming  may  be  best  done  while  holding  the 
specimen  in  the  left  hand  and  striking  a  quick  blow  with  a  light 
hammer,  so  as  to  chip  off  small  pieces.     Remember,  the  sharper 
the  blow,  the  less  liable  is  the  specimen  to  shatter.     The  last  of 
the  dressing  may  be  done  by  striking  the  specimen  square  on  the 
edge.     This  is  especially  practicable  with  quartzose  and  all  crys- 
talline rocks.     Fossils  should   be  worked  out  of  the  rock  with 
hammer  and  chisels  and  other  appropriate  tools,  or  at  least  the 
adhering  rock  should  be  as  much  removed  as  possible. 

6.  When  specimens  are  to  be  boxed  for  transportation,  wrap 
each  separately  in  paper,  and  use  enough  packing  material  of 
paper,   hay  or   straw,  to    prevent   rubbing   against    each   other. 
Always  fill  the  box  as  full  as  possible.     If  the  specimens  will 
not  do   it,   use  waste   paper,   sawdust  or   anything  —  even   fine 
chips  —  to  fill  all  the  empty  spaces. 


STANDARD  SAMPLES  OF  MINERALS  AND  ROCKS. 

[To  illustrate  WinchelPs  "Geological  Excursions."] 

The  whole  list  forms  "Collection  No.  1."     The  list  omitting  the 
starred  names  forms  "  Collection  No.  2." 


1.  Quartz  (at  least  one  crystal  with 

termination). 

2.  Chalcedony  or  Agate. 

3.  Red  Jasper. 

4.  Hornstone  or  Chert. 

5.  Orthoclase,    showing    crystalline 

form. 

6.  Labradorite. 

7.  *Albite,    or  at  least  some  third 

feldspar. 

8.  Muscovite  (common  mica),  show- 

ing crystalline  form. 

9.  Hornblende.    Dark  variety,  show- 

ing crystalline  form. 

10.  *Actinolite. 

11.  Augite,  common  variety,  show- 
ing crystalline  form. 

12.  Talc,  foliated  variety. 

13.  Calcite,  rhombohedral  and  dog- 
tooth varieties. 

14.  *Pyrites. 

15.  *Selenite. 

16.  *Hematite. 

17.  ^Magnetite. 

18.  *Limonite. 

19.  Quartzite,  vitreous. 

20.  Quartzite,  granular. 

21.  Quartzose  Conglomerate. 

22.  Sandstone,  gray. 

23.  *Sandstone,  red. 

24.  Granulite  (Quartz  and  Feldspar). 

25.  Granite   (Quartz,    Feldspar  and 
Mica),  strictly  unstratified. 


26.  Gneiss,  distinctly  stratified. 

27.  Mica  Schist. 

28.  Hydromica  Schist. 

29.  Hornblende  Rock  (Amphibolite). 

30.  Hornblende  Schist. 

31.  Syenite   (Quartz,   Feldspar   and 
Hornblende)  strictly  unstratified. 

32.  Syenitic  Gneiss,  distinctly  strati- 
fied. 

33.  Hyposyenite     (Orthoclase      and 
Hornblende). 

34.  Diorite  (Plagioclase  and   Horn- 
blende). 

35.  Diabase  (Plagioclase  and  Augite). 

36.  *Dolerite. 

37.  *Modern  Lava. 

38.  *Epidote     Rock     (or     Epidotic 
Rock). 

39.  *Talc  Rock  or  Steatite. 

40.  Serpentine. 

41.  Argillite  or  Slate. 

42.  Shale,  argillaceous. 

43.  *Kaolin. 

44.  *Petrosilex      (Cryptocrystalline, 
Quartz  and  Orthoclase). 

45.  Felsite  (Cryptocrystalline,  Quartz 
and  Plagioclase). 

46.  Porphyritic  Rock. 

47.  *Marl. 

48.  Common  Limestone,  with  Fos- 
sils. 

49.  Marble  (Crystalline  Limestone). 

50.  Dolomite. 


11 


12     .         STANDARD   SAMPLES   OF   MINERALS   AND    ROCKS. 

1223  BELMONT  AVENUE, 
PHILADELPHIA,  PA.,  January  8,  1884. 

1  agree  to  supply  suitable  standard  specimens,  according  to  the  foregoing 
list,  for  schools  using  WinchelPs  "Geological  Excursions" — the  rock  speci- 
mens to  be  dressed  to  cabinet  shape,  and  all  to  be  permanently  labelled,  and 
delivered  in  Philadelphia  according  to  directions,  for  the  following  prices : 

For  "Collection  No.  1,"  Students'  size,  $3.00;  Teacher's  size,  $5.00. 
For  "Collection  No.  2,"  Students'  size,  $2.00;  Teacher's  size,  $3.50. 
For  Fragments,  or  undressed   specimens,    "Collection- No.   1,"  $1.50; 
"No.  2,"  $1.00. 

Extra  for  compartment  tray  (if  ordered)  with  lid,  as  follows: 

Pasteboard  Tray,  No.  1,  Students'  size,  $1.00;  Teacher's  size,  $1.50. 
No.  2,  Students'  size,  $0.75;  Teacher's  size,  $1.15. 
For  Fragments,  "No.  1,"  75  cents;  "No.  2,"  50  cents. 

With  sides  and  top  of  black  walnut,  double  the  above  prices.* 

A.  E.  FOOTE. 

*The  "fragment"  collections  may  be  sent  by  mail— the  "Collection  No.  1 "  for 
about  35  cents,  and  ".No.  2"  for  about  25  cents. 


GEOLOGICAL  EXCURSIONS. 


EXCURSION   L— In  the  Garden. 
Organic  and  Inorganic. 

T  ET  us  step  into  the  garden.  Here  is  a  gravel  walk  ;  its 
-*-*  surface  is  covered  with  small  rounded  stones.  If  it  is 
not  a  gravel  walk  we  can  at  least  find  a  few  small  stones  in 
it.  These  stones  do  not  grow,  like  asparagus  and  roses. 
They  do  not  take  food  of  any  kind  ;  they  do  not  see  or  feel 
as  we  tread  upon  them.  Here  are  some  plants.  Probably 
they  do  not  see  or  feel ;  but  they  grow,  and  they  take  in 
nourishment  through  their  roots  and  leaves  to  enable  them 
to  grow.  Here  is  a  toad,  sheltering  himself  under  the 
leaves  of  the  plant.  He  is  waiting  till  sunset,  when  he 
will  hop  out  and  search  for  insects  to  eat.  The  toad  also 
feeds  and  grows ;  and  in  addition  he  sees  and  feels. 

We  say  the  plant  and  the  toad  and  the  insect  are  organic  ; 
because  they  have  organs  or  parts  which  enable  them  to  do 
all  the  various  things  which  their  lives  require.  State  what 
some  of  those  things  are.  The  power  to  do  one  of  these 
things  we  call  a  function.  The  heart  is  an  organ  whose 
function  is  to  propel  the  blood  through  the  blood  vessels. 
What  is  the  function  of  the  teeth  ?  Every  organ  has  some 
function.  But  the  stone  has  no  organs,  and  it  performs  no 

13 


1*  GEOLOGICAL   EXCURSIONS. 

functions.  It  simply  lies  still,  and  permits  the  atmosphere, 
the  rains  and  the  frosts  and  the  sun  to  do  all  they  can  to 
dissolve  it,  or  crumble  it  to  powder,  and  cause  it  to  waste 
away.  It  is  inorganic.  It  has  neither  mouth  nor  legs,  nor 
liver,  nor  any  other  organs.  If  we  should  examine  it  with 
a  microscope,  we  should  not  be  able  to  find  any  cells,  or 
fibres,  or  membranes,  or  vessels,  as  we  would  in  a  plant  or 
an  animal.  The  stone  is  very  similar  all  through,  from 
side  to  side.  So  we  see  a  great  difference  between  an  inor- 
ganic body  and  an  organic  body.  The  substances  of  which 
an  inorganic  body  is  composed  are  called  mineral  sub- 
stances. The  chemist  tells  us  that  an  organic  body  is  also 
composed  of  mineral  substances ;  but  the  difference  is  that 
in  the  organic  body  the  substances  are  made  first  into  com- 
pounds which  do  not  exist  in  the  inorganic  body,  and  these 
are  then  made  into  organs,  which  are  also  wanting  in  the 
inorganic  body. 

All  organic  bodies  have  life,  or  have  had  life.  An  or- 
ganic body  when  dead  is  still  organic  until  it  is  decomposed. 
Its  parts  are  then  inorganic.  Organic  beings  may  produce 
substances  which  have  no  organic  structure  —  such  as  sap, 
spider's  web,  perspiration  and  dandruff.  These  are  organic 
products,  and  are  therefore  organic. 

EXERCISES. 

Name  several  organic  bodies.  Name  several  sorts  of  inor- 
ganic bodies.  In  what  respect  is  a  silver  coin  like  a  stone  ? 
Is  a  stone  organic  or  inorganic  ?  Is  the  head  on  the  coin 
organic  or  inorganic  ?  How  is  it  with  a  board  ?  a  pen  ?  the 
outer  dead  bark  of  a  tree?  a  linen  handkerchief?  a  silk  dress? 


IN   THE   GARDEN    AND   FIELD.  15 

a  dinner  plate  ?  a  potato  ?  a  dish  of  mashed  potatoes  ?  the 
breath  from  your  nostrils  ?  a  dead  leaf  ?  an  extracted  tooth  ? 
milk  ?  beer  ?  molasses  ?  clay  ?  paper  ?  a  squash  ?  the  same 
squash  mashed  for  dinner?  the  ashes  from  a  coal  fire?  the 
ashes  from  a  wood  fire  ?  lemonade  ?  a  pocket  knife  ?  an  oyster 
shell  ?  a  peach  stone  ?  the  sting  of  a  bee  ?  a  loaf  of  bread  ?  a 
loaf  of  bread  burned  to  ashes  ?  a  dead  bird  ?  chewing  gum  ? 
hair  of  a  mouse  ?  gelatine  ?  stove-mica  ?  lamp  smoke  ?  air  ? 
Which  are  more  abundant,  organic  things  or  inorganic  things? 
Which  are  more  useful  ?  Which  decay  more  easily  ?  Are  you 
organic  or  inorganic  ?  Is  there  any  mineral  matter  in  your 
composition  ?  In  what  respects  do  you  resemble  a  stone  ?  In 
what  do  you  differ  from  a  stone  ? 


EXCUKSION  II.— In  the  Garden  and  Field. 
Boulders  and  Sand. 

Let  us  go  into  the  garden  again.  Look  very  carefully  at 
the  gravel  on  the  walk.  Here,  where  there  is  no  gravel 
walk,  we  still  see  some  little  stones  just  like  those  which 
form  gravel.  The  stones  are  of  various  sizes.  Some  are  so 
small  that  we  might  call  them  grains  of  sand ;  and  some  are 
large  enough  to  be  called  pebbles.  Still  others  are  so  large 
as  to  be  called  cobble  stones,  and  are  sometimes  used  to 
pave  streets,  or  at  least,  to  pave  the  gutters  along  the  sides 
of  tho  streets.  The  little  stones  which  the  boys  throw  are 
rounded  pebbles;  the  larger  ones  which  they  use  to  crack 
nuts  are  cobble  stones. 

But  then,  what  is  the  difference  between  a  cobble  stone 
and  one  of  those  larger  rounded  stones  in  the  field  or  by  the 
roadside  which  a  boy  could  scarcely  lift?  —  or  even  those 


16  GEOLOGICAL   EXCURSIONS. 

still  larger  ones  which  a  man  could  not  lift  ?  Is  there  any 
difference  except  in  size?  Let  us  examine  some  of  them. 
We  must  go  into  the  field.  There  is  no  difference.  If  we 
inspect  grains  of  sand,  we  see  that  most  of  them  are  light- 
colored  when  washed  clean.  But  many  are  stained,  and 
some  are  brown,  and  some  are  even  black.  Different  grains 
thus  differ  among  themselves. 

Now  collect  a  lot  of  pebbles.  You  see  that  they  differ  in 
the  same  way  as  the  grains  of  sand.  Only  you  see  some 
pebbles  which  seem  to  be  made  up  of  different  sorts  of 
mineral  matters.  Some  look  as  if  a  great  many  grains  of 
sand  had  been  stuck  together  to  form  a  cobble  stone.  Each 
different  kind  is  a  separate  mineral.  Most  of  the  large, 
loose  rocks  in  the  field  present  the  same  appearance.  Some- 
times a  larger  stone  seems  to  be  made  of  several  pebbles. 

Well,  if  we  turn  now  from  the  larger  to  the  smaller  again, 
you  will  find  some  of  these  grains  of  sand,  on  close  examin- 
ation, to  be  composed  of  different  mineral  materials.  Let 
us  select  a  number  of  such  grains.  You  may  know  them  by 
the  difference  of  color  in  different  parts  of  the  grain.  How 
many  colors  in  this  grain  ?  How  many  in  the  next  one  ? 
What  colors  are  they? 

Of  course,  the  stones  larger  than  pebbles  and  cobble 
stones  generally  contain  various  mineral  substances  also. 
Let  us  examine  some  of  these  stones.  Here  is  one  in  which 
we  can  detect  much  white  rock,  together  with  some  pink  and 
some  smoky.  Here  is  one  with  white  and  cream  color  and 
black.  Here  is  one  with  two  kinds  of  white  and  also  black. 
Here  is  one  full  of  red  rounded  spots  or  pebbles,  with  some 


IN   THE    GARDEN    AND    FIELD.  17 

smaller  dark-colored  ones,  and  many  white  or  glassy  ones. 
Here  is  a  large  rounded  rock  with  white  grains  of  two  kinds 
and  black  grains  of  two  kinds. 

Now,  perhaps,  where  you  are  you  will  not  find  exactly 
such  kinds  and  such  mixtures  of  minerals  as  these,  but  you 
will  find  some  kinds.  You  can  also  tell  what  colors  they 
are  and  how  they  are  mixed.  Do  not  fail  to  tell  all  that  you 
can.  How  many  colors  or  kinds  of  minerals  can  you  find 
all  together  ?  Are  the  separate  minerals  always  rounded  ? 
Are  the  separate  minerals  ever  angular  like  grains  of  coarse 
salt?  See  if  you  can  find  rocks  with  the  same  mineral  colors 
as  I  have  just  mentioned. 

Well,  all  these  rounded  stones  are  called  boulders.  Some 
stones  are  not  boulders.  All  stones  taken  from  quarries  are 
not  boulders.  All  stones  which  have  been  broken  from  a 
ledge  of  rock  not  far  away  are  not  boulders.  You  may 
know  a  boulder  by  its  rounded  and  smoothed  appearance, 
and  by  the  fact  that  it  is  a  different  kind  of  rock  from  any 
ledges  or  quarry  stones  in  the  neighborhood.  Would  you 
call  a  boy's  pocket  marbles  boulders? 

In  some  regions  there  are  no  stones  to  be  found  except 
boulders.  This  is  the  case  in  some  parts  of  the  western 
states.  In  the  Lower  Peninsula  of  Michigan  there  are  very 
few  ledges  of  rocks ;  and  the  people  sometimes  break  up 
boulders  for  building  stones.  Sometimes  boulders  are  large 
enough  to  weigh  fifteen,  twenty  or  even  hundreds  of  tons. 
In  New  Hampshire  and  Vermont  are  many  enormous  boul- 
ders. Here  is  a  picture  of  one  in  New  Hampshire,  which  is 
46  feet  long,  24  feet  wide,  and  26  feet  high.  You  see  a 


18 


GEOLOGICAL   EXCURSION'S. 


FIG.  1.— GREAT  BOULDER  NEAR  GILSUM,  N.  H. 
(C.  H.  HITCHCOCK.) 


school  house  in  the 
shelter  of  the  rock.  A 
piece  33  feet  long  and 
10  feet  wide  was  split 
off  by  frost  in  1817. 
The  whole  stone  be- 
fore splitting  contain- 
ed 32,000  cubic  feet, 
and  weighed  2,286 
tons.  Far  away,  a 


thousand   miles   from 
this,  large  boulders  are  equally  abundant.    Here  in  Figure  2, 


FIG.  2. —  GREAT  BOULDER  OF  PORPHYRY  AT  ST.  IGNAOE,  LAKE  SUPERIOR, 

(PHOTOGRAPH.) 


IN   THE   GARDEN    AND    FIELD.  19 

is  a  view  of  one  at  St.  Ignace,  Lake  Superior.  It  is  composed 
of  porphyry,  and  is  25  feet  high.  Notice  how  it  is  rounded. 
You  can  see  also,  that  the  region  abounds  in  smaller  boulders. 
In  most  parts  of  New  England  large  and  small  boulders  are 
everywhere  to  be  found.  Here  in  Figure  3  is  a  view  near 


FlG.  3. — A    BOULDER-COVERED    FlELD    NEAR    GLOUCESTER,  MASS.   (SlEELE.) 

Gloucester,  Massachusetts.  In  Connecticut,  in  the  neigh- 
borhood of  Long  Island  Sound,  some  regions  are  so  thickly 
overspread  that  one  can  cross  a  field  without  touching  the 
ground.  On  the  contrary,  there  are  some  regions  where  no 
boulders  are  to  be  found.  There  are  very  few  on  the  prairies 
of  Illinois.  There  are  none  south  of  Virginia,  Kentucky 
and  Missouri.  In  some  of  the  southern  states  also,  there 
are  almost  no  ledges  of  rocks ;  and  the  people  have  no 
building  stones  except  such  as  are  brought  from  a  great  dis- 
tance. But  almost  everywhere  some  pebbles  may  be  found. 
Now,  one  thing  more.  Examine  this  soil.  What  does 
it  seem  to  be  composed  of?  It  is  partly  fine  and  partly 


20  GEOLOGICAL   EXCURSIONS. 

coarse.    Let  us  try  an  experiment.     Take  a  tall  glass  vessel, 
or  even  a  clear  glass  bottle  or  fruit  jar,  and  stir 
a  handful  of  soil  in  the  vessel  full  of  water. 
There,   how  muddy  the  water  becomes!  —  but 
most  of  the  matter  sinks  quickly  to  the  bottom. 
Some,    however,    settles    slowly.      Watch    it. 
Now  we  have  a  handful  of  soil  assorted.     The 
coarser  parts  are  at  the  bottom  ;    the  coarse 
sand  is  above  these  ;  the  fine  sand  next,  and 
the  particles  of  mud  are  floating  in  the  water. 
FIG.  4.          We  will  pour  off  the  muddy  water  and  fill  the 
ASSORTMENT      vessel  again  with  clear  water.     The  water  is 
IN  THE  SOIL.     st^  stained  ;    but  most  of  the  matter  in  the 
vessel  can  now  be  seen  to  consist  of  sand,  with 
a   few  small   pebbles.     Is  it  possible  ?     The  soil   itself  is 
almost  wholly  composed  of  mineral  substances,   which  do 
not  differ  from  pebbles  except  in  being  finer.     These  finest 
substances  and  the  coarser  all  belong  to  one  class.     What- 
ever made  the  larger  boulders  and  the  pebbles,  made  also 
the  principal  part  of  the  whole  soil. 

EXERCISES. 

What  was  the  mud  composed  of  which  we  poured  off  with  the 
water?  Did  it  consist  chiefly  of  still  finer  mineral  substances? 
Are  there  any  organic  substances  in  the  soil?  What  is  the 
reason  for  your  answer?  What  could  be  the  origin  of  any 
organic  substances  in  the  soil  ?  Do  the  roots  of  plants  use  any- 
thing in  the  soil?  What  is  the  use  of  the  soil  to  a  tree  except 
to  support  it  just  like  a  fence  post?  If  plants  use  anything  in 
the  soil,  do  they  use  it  in  a  solid  state  or  in  a  state  of  solution  ? 
What  substances  may  serve  as  food  for  plants?  Do  any  of  these 


TO   THE   GKAVEL  BANK.  21 

come  from  the  mineral  matters  in  the  soil?  Would  plants  grow 
in  a  soil  composed  of  clean  sand?  Why  do  you  answer  thus? 
Do  you  suppose  the  grains  of  sand  were  ever  parts  of  larger 
mineral  masses  ?  Could  you  make  sand  out  of  a  pebble  ?  Could 
you  make  mud  from  a  pebble?  Are  these  pebbles  undergoing 
any  changes?  Are  there  any  causes  which  reduce  them  slowly 
to  the  condition  of  sand  and  mud?  Take  this  pebble  home  and 
bring  it  back  as  mud.  What  is  a  brick  made  of  ?  Is  clay  in  any 
respect  like  mud?  How  was  the  brick  made  so  hard?  Is  the 
brick  a  rock?  Do  you  think  any  of  the  rocks  may  have  been 
made  of  mud  originally?  Can  you  think  of  one  way  in  which 
the  mud  and  gravel  could  have  been  hardened  into  rocks?  Are 
there  any  boulders  about  the  place  where  you  live  ?  How  many 
kinds  of  boulders  can  you  bring  from  your  garden?  Try  it;  and 
if  a  boulder  is  too  large,  bring  a  piece  of  it. 


EXCURSION  III.— To  the  Gravel  Bank. 
The  Drift. 

Let  us  make  an  excursion  to  some  gravel  bank.  We 
may  find  it  alongside  of  the  river  or  brook,  where  the 
stream  flows  close  to  the  high  land.  Or  we  may  find  it 
on  the  railroad  in  the  "  deep  cut."  Or  just  in  the  border  of 
the  town,  where  the  authorities  obtain  gravel  to  spread  on 
the  streets,  or  the  masons  dig  for  sand  for  making  mortar. 
Somewhere  is  a  gravel  bank.  Here  it  is.  (See  Fig.  5.) 

This  is  a  common  gravel  bank.  Here  is  the  soil  at  top, 
such  as  we  found  in  the  garden ;  but  in  this  place  we  see 
what  lies  beneath  the  soil.  First,  we  have  the  subsoil, 
which  is  very  commonly  of  a  yellowish  or  reddish  color,  and 
is  apt  to  have  many  gravel  stones  and  pebbles  scattered 


22  GEOLOGICAL   EXCURSIONS. 

through  it.  The  subsoil  is  indicated  by  a  a  a  a.  In  one 
place  we  see  a  deep  funnel-shaped  prolongation  downward, 
which  is  perhaps  a  place  once  filled  by  the  tap  root  of  some 
tree  which  grew  there.  The  subsoil  shows  very  little  strati- 
fication. That  is,  it  is  not  arranged  in  layers.  Beneath  the 
subsoil  we  find  beds  of  gravel  stones  and  fine  sands  ar- 
ranged in  irregular  layers,  which  constitute  a  confused  strati- 
fication. First,  we  see  some  gray  gravel  beds,  b  t>  £,  which 
incline  in  diiferent  directions.  Then  we  come  to  a  thick  bed 
of  pale  buff  fine  sand,  c  c  c  c,  which  is  pretty  evenly  strati- 
fied, with  the  thin  layers  or  laminae  nearly  horizontal.  Be- 
neath this  is  a  course  of  pebbles,  d  d  d,  and  at  e  e  e  is 
another  course.  Between  them  is  a  stratum  of  pebbly  sand 
which  is  obliquely  laminated.  Below  e  e  is  a  bed  of  gravel, 
f  f  ft  quit6  distinctly  laminated,  but  with  the  laminae  in- 
clining toward  the  left  instead  of  the  right.  At  g  g  is  a  bed 
of  coarse  sand,  with  laminse  inclining  toward  the  right.  It 
reaches  up  and  partially  blends  with  the  gravel  stratum  be- 
tween d  and  e.  At  A  A  is  another  stratum  of  fine  buifish 
sand,  with  lamination  inclined  steeply  to  the  right.  All 
these  bands  and  strata  are  distinguished  by  differences  in 
coarseness  and  by  differences  in  color.  At  the  foot  of  the 
bank  is  a  sloping  pile  of  sand,  i  i  i,  which  has  run  down 
from  above.  In  one  place,  j,  is  a  collection  of  lumps  of 
red  subsoil  fallen  down  from  the  top.  A  sloping  bank  of 
rubbish  at  the  foot  of  a  bluff  of  gravel  or  rocks  is  called 
a  talus.  Often  we  find  cobble  stones  along  the  foot  of  the 
bluff  which  have  rolled  out  of  the  bank  above.  These  are 
sometimes  iron-stained  ;  sometimes  covered  by  a  white  crust, 


TO   THE   GRAVEL   BANK. 


24  GEOLOGICAL    EXCURSIONS. 

which  holds  gravel  stones  cemented  to  the  larger  stones. 
This  crust  is  a  precipitate  of  calcium  carbonate.  This  will 
be  explained  hereafter. 

This  fine  example  of  a  gravel  bluff  simply  illustrates 
what  may  be  found  on  almost  every  square  mile  of  the 
northern  states.  This  view  is  129  feet  above  the  bed  of  the 
Huron  River,  and  204  feet  above  the  bed  rock,  which  has 
only  been  found  by  boring.  On  the  bed  rock  the  drift  is 
found  to  be  a  heavy  mass  of  unstratified  clay,  with  many 
large  boulders  dispersed  through  it.  At  other  localities 
this  bottom  boulder  clay  is  found  exposed  at  the  surface. 

We  may  find  these  loose  materials  lying  upon  the  sur- 
face in  all  parts  of  the  northern  states.  The  depth  varies 
from  nothing  to  one,  two  or  three  hundred  feet.  It  is  won- 
derful that  by  any  means  such  an  enormous  amount  of  loose 
materials  could  have  been  spread  over  the  country.  The 
sands  and  clays  are  generally  somewhat  assorted,  and  ar- 
ranged irregularly  in  separate  layers.  Can  you  not  recall 
some  railroad  cut  where  this  assortment  is  shown  ?  Such 
arrangement  is  known  as  stratification,  and  the  separate 
layers  are  strata.  When  we  wish  to  speak  of  one  layer  it 
is  a  stratum.  Sometimes  the  finer  materials  have  been 
completely  removed,  and  we  find  only  a  bed  of  pebbles  and 
large  boulders,  as  at  many  places  in  Massachusetts.  Visit- 
ors to  Martha's  Yineyard  may  find  such  a  coarse  deposit 
at  many  points  along  the  beach.  All  these  loose  materials 
scattered  over  the  northern  states  are  Drift.  The  whole 
extent  of  the  deposit  forms  the  Drift  formation. 

Along  the  shores  of  the  ocean  and  the  Great  Lakes  the 


TO   THE   GRAVEL   BANK.  25 

sands  are  washed  out  by  the  action  of  the  waves  in  certain 
places,  and  transported  and  deposited  again  in  more  pro- 
tected places.  Sometimes  two  habitual  movements  conflict- 
ing with  each  other  cause  the  drifting  sands  to  be  deposited 
in  enormous  banks  and  sandy  sloping  beaches.  When  dried, 
the  winds  sometimes  lift  the  fine  sands  which  have  been  left 
high  along  the  beach,  and  drive  them  inland.  Thus  are 
formed  piles  of  dry  sand  called  dunes  or  downs.  The  wind 
continues  to  drive  the  sand  forward,  and  so,  fertile  fields, 
gardens,  houses  and  forests  are  sometimes  buried  beneath 
it.  At  the  south  end  of  Lake  Michigan — especially  about 
Michigan  City  —  maybe  seen  some  enormous  sand  dunes. 
At  Grand  Haven  the  sand  buried  the  railroad  track,  fences 
and  buildings,  and  the  station  had  to  be  removed  to  the 
opposite  side  of  Grand  River. 

EXERCISES. 

What  is  the  nature  of  the  surface  of  Cape  Cod?  Can  you 
imagine  how  Cape  Cod  may  have  been  formed?  Is  Cape  Cod 
extending  or  diminishing?  Can  you  think  of  any  other  sandy 
cape  forming  in  a  similar  way?  What  is  Sandy  Hook?  Are 
there  any  sand  dunes  on  the  coast  of  New  England?  What  is 
the  connection  between  dunes  and  the  prevailing  direction  of  the 
wind  ?  Why  are  there  so  many  dunes  on  the  east  shore  of  Lake 
Michigan  and  none  on  the  west  ?  What  is  the  prevailing  direc- 
tion of  the  wind  in  the  northern  states?  Should  there  be  any 
sand  dunes  on  the  coast  of  California  ?  What  is  the  fact  in  the 
case?  Should  there  be  any  on  the  east  side  of  Chesapeake 
Bay  ?  What  is  the  source  of  the  materials  which  so  suddenly 
form  bars  and  new  islands  in  the  Mississippi  River?  Do  you 
know  of  any  bed  rocks  which  are  not  covered  with  Drift  ? 
Where  are  they  ?  Why  does  the  Drift  not  cover  them  ?  Are  all 


26  GEOLOGICAL   EXCURSIONS. 

bed  rocks  ledges  ?  Are  all  ledges  bed  rocks  ?  Why  is  there  so 
little  vegetation  on  sandy  surfaces?  What  is  the  desert  of 
Sahara?  Is  there  any  way  to  prevent  the  drifting  of  the  sands 
from  dunes  ?  Now  make  a  sketch  of  the  sand  bank  or  gravel 
bluff,  and  bring  it  to  the  next  meeting  of  the  class. 


EXCURSION   IV.— To  Another   Gravel  Bank. 
Springs  and  Wells. 

Let  us  go  to  another  bank.  It  may  be  very  near  the 
first.  Here  is  a  little  difference.  A  spring  of  pure  water 
issues  from  the  bank  and  trickles  down  the  slope.  Just 
underneath  the  spring  is  a  bed  of  clay,  and  all  the  bank 
above  is  composed  of  loose  materials.  The  clay  bed  or 
stratum  can  be  traced  in  both  directions  some  rods,  and 
it  is  seen  to  show  a  concave  depression  at  the  spring.  The 
water  issues  from  a  small  opening  which  has  been  worn 
by  the  flow.  Now  it  is  plain  that  when  the  rain  falls  on 


FIG.  6. —  GRAVEL  BANK  AND  SPRING. 


TO  ANOTHER  GRAVEL  BANK.  27 

the  surface  of  the  ground,  it  soaks  downward  through  the 
gravel  as  far  as  this  dish  of  clay.  Then  it  follows  along 
the  surface  of  the  clay  toward  a  lower  level.  In  this  case 
its  course  leads  directly  to  the  face  of  the  bank,  and  when 
it  reaches  that,  the  water  issues  as  a  spring.  Suppose  we 
go  to  the  top  of  the  bank  and  dig  a  well  at  a  point  not 
too  far  back  ;  when  we  reach  the  clay  stratum  we  shall 
find  the  water  resting  on  it,  and  the  water  will  flow  into 
the  well.  If  the  clay  stratum  were  not  there  we  should 
have  no  spring  and  no  well.  But  there  is  probably  an- 
other clay  stratum  at  some  greater  depth,  and  undoubtedly 
water  would  be  found  resting  on  that.  So  a  well  might 
be  obtained  by  digging  deeper.  There  are  many  gravel 
banks  where  several  clay  beds  may  be  seen,  or  found  by 
digging.  But  they  seldom  continue  uninterrupted  for  great 
distances.  Nor  are  they  parallel  with  each  other.  They 
overlap  each  other  in  every  fashion  and  are  inclined  in 
various  ways. 

Suppose  some  stones  or  substances  exist  in  the  gravel 
bank  which  are  capable  of  being  dissolved  in  water  —  like 
salt  or  limestone  or  gypsum  or  iron  oxide.  Then  the  water 
which  issues  at  the  spring  will  be  a  solution  of  such  sub- 
stances. The  water  will  be  a  mineral  water  more  or  less 
strong. 

Many  times  the  water  dissolves  some  substance  in  one 
place  and  then  deposits  it  in  another.  Some  mineral  is 
very  frequently  deposited  by  the  water  where  it  escapes  at 
the  spring.  This  is  because  water  generally  cannot  hold 
so  much  mineral  in  solution  when  exposed  to  the  air  as 


GEOLOGICAL   EXCURSIONS. 


it  can  while  confined  deep  in  a  gravel  bed.  In  New  York 
and  the  Western  States  spring  waters  often  deposit  large 
amounts  of  matter  consisting  chiefly  of  limestone  that  had 
been  dissolved  in  the  earth.  The  matter  is  not  all  thrown 
down  or  precipitated  until  the  water  has  flowed  several 
rods.  If  the  water  flows  over  a  hard  sloping  surface,  it 
deposits  a  hard  crust  which  continues  to  grow  until  some- 
thing similar  to  a  bed  of  limestone  is  formed.  "We  call  it 
travertin.  In  some  countries  it  forms  extensive  beds 
which  are  quarried  for  building 
purposes.  If  the  water  flows  over 
flat  ground  and  stands,  the  deposit 
is  spongy  and  irregular,  and  we  call 
it  calcareous  tufa.  Often  it  is 
mixed  with  earth  and  stones. 
Sometimes  the  stems  of  mosses  and 
dry  leaves  and  sticks  and  bones  of 
animals  become  incrusted  with  it. 
Some  very  beautiful  specimens  of 
so  called  "petrified  moss"  are  pro- 
duced. If  the  water  is  collected  in 
a  pond  or  lake  the  deposit  falls  to  the  bottom  and  forms 
a  white  powdery  layer  which  we  call  marl.  Here  it 
becomes  mingled  with  dead  shells  of  molluscs  which 
lived  in  the  pond  or  lake,  and  thus  forms  shell  marl. 
These  shells  are  real  fossils.  Sometimes  shell  marl  be- 
comes quite  dry  and  hard.  It  is  then  extremely  like  a 
common  limestone  with  fossil  shells  in  it.  Water  which 
contains  limestone  in  solution  is  called  hard.  In  many 


FIG.  7. — "PETRIFIED 
Moss." 


TO   ANOTHER   GRAVEL   BANK.  29 

parts  of  New  England  there  are  no  limestones  in  the 
gravel  deposits;  and  hence  no  "  hard  "water  is  produced. 
The  water  of  wells  and  springs  is  there  soft. 

Besides  limestone  there  is  often  iron  oxide  in  the  earth 
to  be  dissolved  by  the  waters  which  circulate  underground. 
Such  waters  are  called  chalybeate.  The  iron  is  sometimes 
deposited  in  marshy  situations,  and  forms  bog  iron  ore. 
Frequently  both  lime  and  iron  are  deposited,  and  the  mix- 
ture forms  a  sort  of  paint  called  ochre.  The  greater  the 
amount  of  iron  the  deeper  the  color.  Also,  when  the  iron 
oxide  is  chemically  combined  with  water,  the  ochre  is 
yellow,  more  or  less  pale;  but  if  it  is  burned  so  as  to 
drive  oif  the  water,  the  ochre  is  of  a  red  color.  Before 
the  paint  can  be  regarded  of  first  quality  it  has  to  be 
ground  very  fine.  Iron  deposits  from  springs  are  common 
in  most  parts  of  the  country.  The  pebbles  and  sand  from 
a  bank  of  drift  are  often  deeply  incrusted  and  even  ce- 
mented together  by  a  deposit  of  iron.  This  is  very  strik- 
ingly shown  along  the  bluff  shores  of  Martha's  Vineyard. 

EXERCISES. 

Can  you  mention  any  chalybeate  spring?  Do  you  know  any 
spring  whose  waters  stain  the  stones  of  a  reddish  color?  Can 
you  point  out  any  bed  of  bog  iron  ore  ?  Are  chalybeate  springs 
much  resorted  to  for  purposes  of  health?  Have  you  ever  seen 
a  bed  of  marl  ?  Of  what  is  marl  chiefly  composed  ?  Where  did 
the  material  come  from  ?  Do  the  rains  increase  or  diminish  the 
amount  of  soluble  matter  in  the  soil  ?  Is  lime  in  any  form  use- 
ful to  vegetation  ?  Is  it  ever  used  by  farmers  ?  Is  it  more  used 
in  the  eastern  or  the  western  states  ?  What  use  may  the  farmer 
make  of  the  marl  which  accumulates  in  the  ponds  and  low 


30  GEOLOGICAL   EXCURSIONS. 

grounds  ?  A  man  dug  a  well  and  found  water  at  the  depth  of 
twenty  feet;  his  near  neighbor  had  to  dig  sixty  feet;  why  was 
that  ?  On  a  gravel  hill  two  hundred  feet  high  the  well  is  only 
fifteen  feet,  while  at  the  foot  of  the  hill  water  is  found  only  by 
digging  fifty  feet;  why  is  that?  Can  you  make  a  diagram 
showing  how  the  materials  are  arranged  to  produce  such  results  ? 
If  I  dig  a  well  in  sand  near  the  sea  shore  and  water  enters  below 
the  sea-level,  why  is  that  water  fresh?  Why  are  some  wells 
lower  in  a  wet  spell  than  in  a  dry  one  ?  Why  do  the  rivers  not 
cease  to  flow  during  a  summer  drouth  ?  Why  does  the  earth 
retain  some  moisture  even  in  the  dryest  weather?  Which  is 
best  to  retain  moisture  in  a  dry  spell,  a  very  clayey  soil,  or  one 
with  a  good  proportion  of  fine  sand  ?  What  is  the  cause  of  the 
crust  which  forms  on  the  bottom  of  the  tea-kettle? 


EXCURSION   V.— To  Our  Laboratory. 
How  Things  are  Put  Together. 

You  know  already  that  many  different  kinds  of  rocks 
exist.  They  are  of  different  colors  and  different  degrees 
of  hardness,  and  they  are  also  different  mixtures  of  min- 
erals. We  are  very  anxious  to  know  more  about  rocks,  so 
as  to  be  able  to  call  each  one  by  its  name.  Most  rocks 
are  mixtures  of  different  minerals,  and  we  must  therefore 
learn  a  little  about  minerals.  But  minerals  are  mostly 
composed  of  two  or  more  substances  or  chemical  elements ; 
and  therefore  we  must  learn  something  about  chemical  ele- 
ments and  the  way  they  combine  with  each  other. 

Now  let  us  perform  a  couple  of  little  experiments. 
First,  take  a  piece  of  chalk  and  drop  a  little  strong  acid 
upon  it.  Vinegar  will  answer  if  strong.  Do  you  see  the 


TO   THE   LABORATORY.  31 

little  bubbles  rise  as  if  the  chalk  were  boiling?  A  drop 
of  water  or  oil  will  not  produce  such  a  result.  This  ia 
chemical  action ;  we  shall  try  to  understand  it. 

Again,  let  us  take  a  vial  of  lime-water.  We  can  pro- 
cure it  of  the  druggist,  or  can  prepare  it  ourselves  by 
shaking  up  some  quick-lime  in  water  and  pouring  off  the 
clear  water  into  a  glass  bottle  after  the  mixture  settles. 
Now  take  a  glass  tube,  which  can  also  be  had  of  the  drug- 
gist ;  or  otherwise  take  a  simple  oat  straw  and  breathe 
through  this  into  the  clear  lime-water.  Do  you  see  the 
white  cloud  which  forms?  Continue  to  do  so  for  two  or 
three  minutes,  and  then  let  the  lime-water  stand  for  some 
time.  There,  do  you  see  the  fine  powder  settling  on  the 
bottom?  It  will  all  fall  down  and  leave  the  liquid  clear 
above.  This  is  also  a  chemical  operation.  Now  let  us  see 
how  it  can  be  explained. 

You  remember  the  stone  which  you  took  and  pounded 
to  a  fine  powder,  and,  by  mixing  a  little  water,  made  into 
mud.  Well,  however  fine  you  made  the  powder,  each 
particle  might,  by  some  means,  be  made  even  smaller. 
We  can  at  least  think  smaller  particles.  But  it  is  com- 
monly believed  that  there  are  really  particles  so  small  that 
it  would  not  be  possible  by  any  means  to  make  them 
smaller.  These  are  called  atoms.  They  are  really  vastly 
finer  than  the  finest  particles  of  the  finest  dust  which  floats 
in  the  air.  If  we  could  take  a  drop  of  water  and  magnify 
it  to  the  size  of  this  earth,  and  magnify  the  atoms  in  it  in 
the  same  proportion,  the  atoms  would  be  about  the  size 
of  small  shot.  All  substances  are  made  up  of  these  minute 


32 


GEOLOGICAL  EXCURSIONS. 


atoms.     Iron  is  made  of  atoms.     Water  is  made  of  atoms. 
The  air  is  made  of  atoms. 

There  are  about  sixty-four  different  kinds  of  atoms 
known.  Iron  contains  one  kind,  sulphur  another  kind, 
silver  another.  The  atoms  of  each  kind  have  a  strong 
attraction  for  certain  other  kinds  of  atoms.  This  is  chem- 
ical affinity.  The  two  kinds  corne  together  when  they  can, 
and  remain  close  together.  This  is  a  chemical  combina- 
tion. So  most  substances  are  compounds  of  different  kinds 
of  atoms.  Water  is  made  of  two  kinds  of  atoms  ;  that  is, 
water  is  a  compound.  But  iron  is  composed  of  only  one 
kind  of  atom  ;  that  is,  iron  is  an  element.  All  the  metals 
are  elements.  Now  there  are  only  sixty-four  elements 
known  in  all  the  great  mass  of  the  earth.  Not  more 
than  thirteen  of  these  are  very  important  in  making  all 
the  rocks.  I  will  give  their  names  because  they  ought  to 
be  learned.  If  we  should  take  100  pounds  of  the  average 
solid  earth,  there  would  be  in  the  mass 


Oxygen, 
Silicon,       . 
Aluminum, 
Iron,  . 

Calcium, 
Sodium,      . 


45  pounds. 

Potassium, 

25 

Carbon, 

10 

Hydrogen, 

8 

Sulphur, 

6 

Nitrogen, 

2i       * 

Chlorine, 

Magnesium,  j 

2  pounds. 


All    together   nearly 
11  pounds. 


In  the  atmosphere  and  in  water  there  are  larger  pro- 
portions of  Nitrogen,  Oxygen  and  Hydrogen. 

Oxygen  has  a  strong  affinity  for  most  of  the  other 
elements,  and  the  compounds  which  it  forms  with  them 
are  called  oxides.  So  chlorine  unites  with  other  elements 


TO   THE   LABOKATORY.  33 

and  forms  chlorides.  We  are  very  familiar  with  many  of 
the  oxides.  Water  is  hydrogen  oxide.  Lime  is  calcium 
oxide.  Caustic  soda  is  sodium  oxide.  Caustic  potash  is 
potassium  oxide.  Iron  rust  is  iron  oxide.  So  common 
salt  is  sodium  chloride.  Now  state  what  these  different 
oxides  and  chlorides  are  composed  of.  Some  compounds 
contain  two  or  three  times  as  much  oxygen  or  chlorine 
or  other  elements  as  other  compounds  contain;  but  we 
cannot  go  so  far  as  to  take  any  account  of  that  at  the 
present  time. 

The  union  of  oxygen  with  certain  elements  results  in 
acid-forming  oxides.  With  other  elements  bases  are 
formed.  The  addition  of  hydrogen  to  the  acid-forming 
oxides  makes  acids  of  them.  The  names  of  the  acids 
most  important  for  us  end  ill  ic.  Thus,  sulphuric  acid,  or 
"oil  of  vitriol,"  is  composed  of  sulphur,  oxygen  and 
hydrogen.  Nitric  acid  is  composed  of  nitrogen,  oxygen 
and  hydrogen.  The  basic  oxides  have  names  which  end 
in  a.  Many  of  them  have  also  old  popular  names.  Thus 
the  oxide  of  potassium  or  potassium  oxide  is  potassa  or 
potash ;  the  oxide  of  sodium  is  soda ;  the  oxide  of  cal- 
cium is  lime ;  one  oxide  of  iron  is  iron  rust. 

Now  please  have  patience  with  a  little  further  explana- 
tion. The  acids  generally  have  strong  affinities  for  the 
bases,  and  the  compounds  which  they  form  are  called 
salts.  When  the  name  of  the  acid  ends  in  ic^  the  name 
of  the  salt  ends  in  ate.  If  sulphuric  acid  unites  with  pot- 
ash the  salt  is  sulphate  of  potash,  or  as  it  is  now  called, 
potassium  sulphate.  So  sulphate  of  soda,  or  sodium  sul- 


34  GEOLOGICAL   EXCURSIONS. 

phate,  is  formed  from  sulphuric  acid  and  soda ;  silicate  of 
lime,  from  silicic  acid  and  lime ;  carbonate  of  lime  (com- 
mon chalk,  marble,  limestone  or  marl)  is  composed  of 
carbonic  acid  and  lime. 

Some  acids  have  stronger  affinities  than  other  acids 
have  for  certain  bases.  Sulphuric  acid  attracts  lime  more 
powerfully  than  carbonic  acid  does.  So  if  we  should  mix 
sulphuric  acid,  carbonic  acid  and  lime  together,  the  lime 
would  be  taken  by  the  sulphuric  acid.  Even  strong  vine- 
gar, which  is  acetic  acid,  would  do  the  same  thing.  More 
than  this,  suppose  carbonic  acid  to  be  already  combined 
with  lime,  forming  chalk ;  then  suppose  a  little  strong 
vinegar  or  sulphuric  acid  to  be  brought  into  contact  with 
the  chalk,  it  seizes  the  lime  and  drives  the  carbonic  acid 
off  with  much  ado.  Carbonic  acid  is  a  gas,  and  that  is 
the  reason  why  its  escape  produces  effervescence.  But  if 
we  introduce  carbonic  acid  into  water  containing  lime  in 
solution,  this  acid  unites  with  the  lime,  forming  carbonate 
of  lime  in  the  water.  As  carbonate  of  lime  is  not  much 
dissolved  by  water,  the  particles  remain  suspended  in  the 
water  for  a  time.  They  finally  settle  down,  however,  as  a 
white  powder.  This  is  of  the  same  nature  as  chalk  and 
marl.  It  is  even  called  precipitated  chalk.  This  is  the 
explanation  of  the  little  experiments  just  made. 

EXERCISES. 

Cut  about  seventy-five  small  square  pieces  of  white  card- 
board. On  ten  of  these  write  a  heavy  capital  O,  which  stands 
for  oxygen.  On  six  of  them  write  H,  which  stands  for  hydro- 
gen. Put  also  the  symbol  of  each  of  the  other  principal  ele- 


TO   THE   LABORATORY.  35 

ments  on  four  others,  thus:  Si  for  silicon,  Al  for  aluminum,  Fe 
for  iron,  Ca  for  calcium,  Na  for  sodium,  K  for  potassium,  C  for 
carbon,  S  for  sulphur,  N  for  nitrogen,  Cl  for  chlorine  and  Mg 
for  magnesium.  Then  put  S  and  O  together,  representing  an 
acid-forming  oxide,  and  to  show  that  it  is  such  add  a  card 
having  on  it  a  cross  made  with  red  ink.  Add  H,  and  you  have 
an  acid.  What  is  the  name  of  it  ?  Then  put  Ca  and  O  to- 
gether representing  a  basic  oxide  ;  and  to  show  this  put  with 
them  a  card  having  on  it  a  cross  made  with  blue  ink.  What 
is  the  name  of  this  base  ?  Then  put  the  acid  and  the  base 
together,  and  tell  what  is  the  name  of  the  salt.  Examine  the 
cards  now  and  see  what  different  elements  enter  into  this  salt. 
With  these  little  cards  illustrate  the  other  combinations  men- 
tioned. Also  those  to  be  mentioned  in  these  exercises. 

Now,  what  caused  the  effervescence  when  we  dropped  a 
little  acid  on  the  chalk  ?  What  is  the  name  of  the  acid  which 
escaped.  Represent  it  with  the  cards.  What  became  of  the 
lime?  Represent  it  with  the  cards.  What  is  the  name  of  the 
salt  formed?  What  became  of  the  carbonic  acid?  When  you 
breathed  in  the  lime-water  what  caused  the  white  cloudiness  ? 
What  was  the  substance  which  fell  to  the  bottom?  Represent 
its  composition  by  means  of  the  cards.  If  oxygen  unites  with 
iron  what  is  the  name  of  the  compound?  Show  me  some  oxide 
of  iron.  When  chlorine  unites  with  sodium  what  is  the  name 
of  the  compound?  What  is  its  common  name?  If  oxygen 
unites  with  aluminum  what  results?  Suppose  silicic  acid  com- 
bines with  alumina,  what  is  the  compound  ?  When  lime-water 
stands  exposed  to  the  air  what  causes  the  crust  which  forms 
on  the  top  ?  Why  does  the  druggist  keep  his  lime-water  close- 
stoppered?  What  complaint  of  the  stomach  is  lime-water  good 
for?  Suppose  you  put  a  little  strong  acid  in  a  bottle  half  filled 
with  water,  and  then  drop  in  some  chalk  and  stop  the  bottle 
tightly,  what  would  result  ?  What,  if  you  should  drop  in  some 
bits  of  marble?  Suppose  pulverized  chalk  and  flour  are  well 
mixed,  and  then  the  whole  is  kneaded  with  vinegar  and  water, 
what  would  result?  Suppose  carbonate  of  soda,  tartaric  acid 


36 


GEOLOGICAL   EXCURSIONS. 


and  flour  are  mixed  and  kneaded  with  water,  what  results? 
Can  we  see  the  atoms  of  matter  with  a  microscope  ?  What 
are  the  components  of  sulphate  of  potassa? 


FIG.  8. — GEOLOGICAL  HAM- 
MER, PALEONTOLOGIST'S 
PATTERN. 


EXCURSION   VI.— To  the  Field. 

Quartz. 

Now  we  will  walk  into  the  field  again,  and  will  take  some 
simple  implements  with  us.  "We  shall  want  first  of  all  one 
or  two  hammers.  If  each  person 
can  have  a  hammer  that  will  be  bet- 
ter. A  good  form  of  geological 
hammer  is  here  shown  in  Figure  8. 
The  pene  a  is  at  right  angles  to  the 
face  1}  and  the  handle.  The  face  is 
flat,  and  a  little  longer  than  broad. 
The  hammer  should  be  of  fine  steel,  with  the  temper  of  a 
stone  mason's  hammer.  The  eye  should  be  large,  and  the 
handle  of  hickory.  For  student's  use  a  hammer  weighing 
from  half  a  pound  to  a  pound  will  be 
most  generally  useful.  But  a  hammer 
weighing  two  pounds  or  more  will 

frequently  be  needed  also.     The  form 
FIG.  9. — GEOLOGICAL  HAM- 
MER, QUARRYMAN'S  PAT-  of  the  regular  stone  mason's  hammer 

(Fig.  9)  is  quite  as  suitable  for  work- 
ing among  very  hard  rocks.  It  is  better  to  use  any  hammer 
which  can  be  had  than  not  to  break  the  rocks  at  all.  We 
shall  want,  also,  a  pointed  piece  of  hard  tempered  steel  to 
test  the  hardness  of  minerals.  A  good  strong  knife  blade 


TO   THE    FIELD.  37 

will  answer  well;  but  if  you  feel  unwilling  to  subject  a  knife 
blade  to  such  use,  you  can  employ  a  simple  implement  like 
Figure  10.  This  is  simply  a  piece  of  steel  rod  flattened  and 
pointed  at  one  extremity,  and  rather  high  tempered.  But 


FIG.  10. — HARDNESS  TESTER. 
a.  View  of  flattened  side  of  point,     b.  View  of  taper  toward  the  point. 

whatever  implement  you  become  accustomed  to  should  be 
used  every  time.  It  will  be  well  to  have  also  a  small  vial 
of  acid  — either  very  strong  vinegar  or  diluted  hydrochloric 
acid. 

Well,  here  we  are  amongst  the  rocks.  Let  us  first  give 
attention  to  the  boulders,  for  we  can  find  more  varieties  of 
rocks  among  them.  We  first  pick  out  a  rock  showing  a 
mixture  of  light  and  dark  colors.  These  are  probably  differ- 
ently colored  minerals.  Now  fix  your  attention  upon  one  of 
these  minerals  and  see  if  you  can  scratch  it  with  your  steel. 
Do  you  say  yes?  Well,  look  at  it  closely,  so  that  when  you 
see  another  piece  of  the  same  kind  you  will  know  it.  See 
if  you  can  find  another  just  like  it.  Well,  does  your  steel 
scratch  it  just  about  as  easily  ?  Try  another  light  colored 
mineral,  does  your  steel  scratch  it  ?  If  not,  this  is  a  harder 
mineral ;  it  is  a  different  mineral.  Your  steel  leaves  a  dark 
line  on  it.  The  mineral  which  you  cannot  scratch  is  quartz. 
But  see,  there  are  several  differently  colored  minerals  which 


38  GEOLOGICAL   EXCURSIONS. 

the  steel  does  not  scratch.  Do  yon  find  them?  They  may 
not  be  all  in  one  stone.  Well,  they  are  all  quartz.  They 
are  different  varieties  of  quartz.  You  will  find  one  variety 
to  be  white  and  opaque  like  porcelain ;  another  will  be  trans- 
parent; another  slightly  rosy;  another  smoky;  another 
almost  black ;  another  brick  red.  That  is,  you  will  be  able 
to  find  all  these  sorts  if  you  examine  different  rocks.  But 
they  all  have  a  glassy  appearance.  Quartz  is  the  hardest 
mineral  you  will  have  to  deal  with.  It  is  hard  enough  to 
scratch  glass.  Besides  its  hardness,  you  may  know  it  by  its 
glassy  lustre.  The  freshly  broken  surfaces  glisten  like  broken 
glass.  Further,  it  always  breaks  with  an  irregular  fracture; 
and  this  is  also  like  glass.  Sometimes  you  find  a  boulder 
composed  entirely  of  quartz.  They  are  generally  white  or 
very  light  colored.  They  are  often  called  "flint  rocks." 
But  flint  proper  has  generally  a  little  duller  lustre,  and  is 
apt  to  be  dusky  or  dark  colored.  The  red  quartz  is  mostly 
red  jasper.  Many  gems  are'  little  else  than  quartz.  This  is 
the  case  with  agate,  amethyst,  carnelian,  chalcedony,  onyx 
and  some  others.  The  colors  are  caused  by  the  admixture 
of  impurities. 

Well,  what  is  quartz  \  It  is  only  silicic  acid  ;  or  we  com- 
monly say  when  this  oxide  is  not  combined  with  the  base,  it 
is  silica.  It  is,  therefore,  composed  of  only  two  elements, 
when  pure.  It  forms  also,  beautiful  crystals  —  beautiful  in 
form  and  beautiful  in  glassy  transparency.  Here  are  some 
quartz  crystals  (Figure  11).  You  see  each  one  has  six 
sides.  It  is  a  hexagonal  prism.  The  sides  may  all  be 
equal;  but  generally  they  are  not  so,  because  more 


TO   THE   FIELD. 


39 


crystalline  matter  has  been  deposited  on  one  side  than  on 
others.  See  also,  how  the  end 
of  the  crystal  tapers  off.  The 
taper  too  is  six-sided.  Some- 
times both  ends  have  such  a  ter- 
mination. Whenever,  in  study- 
ing minerals,  you  find  a  very  hard 
glassy  mineral  which  is  not  so 
broken  but  that  you  can  detect  a 
portion  of  such  a  form  as  this, 

that     circumstance     is     probable  FIG.  11.— A  GROUP  OF  CRYSTALS 

/.  ,1        ,  i  .         i    .  OF  QUARTZ. 

proof  that  the  mineral  is  quartz. 

If,  in   addition,   it   has  a  glassy  lustre   and    the   hardness 
of  quartz,  the  proof  is  conclusive. 

Let  us  see  now  how  many  varieties  of  quartz  we  can  col- 
lect. Break  the  boulders  to  pieces,  and  save  the  pieces 
which  contain  minerals  too  hard  to  scratch.  It  is  very 
necessary  to  know  quartz  in  all  its  conditions — whatever  its 
color,  however  mixed  with  other  substances.  When  you 
can  identify  quartz  with  certainty,  and  distinguish  it  from 
two  other  white  minerals  next  to  be  considered,  you  have 
made  excellent  advancement. 

EXERCISES. 

Look  over  the  small  pebbles  before  collected,  and  see  whether 
any  quartz  exists  among  them.  Are  any  of  them  composed 
wholly  of  quartz?  Examine  this  washed,  clean  sand  and  say 
whether  the  grains  appear  to  be  quartz.  What  proportion  of  all 
the  grains  may  be  considered  quartz?  Try  some  sand  from 
another  location,  and  ascertain  whether  as  large  a  proportion  is 


40  GEOLOGICAL   EXCLUSIONS. 

quartz.  Is  the  fine  sand  which  makes  up  the  greater  part  of  the 
garden  soil  quartz  ?  Is  it  true  then,  that  quartz  forms  the  greater 
part  of  the  drift  ?  Are  these  grains,  pebbles  and  other  boulders 
angular  or  rounded  ?  Were  they  always  as  they  are  now  in  this 
respect  ?  Does  it  appear  that  they  have  been  worn  ?  Why  are 
they  not  worn  completely  to  powder?  Why  are  there  so  few 
boulders  of  rocks  less  hard  than  quartz  ?  Look  at  this  boulder 
with  a  white  streak  through  it ;  is  that  quartz  ?  Is  there  any 
quartz  in  the  rock  besides  this  vein  f  What  makes  this  white 
vein  project  above  the  general  surface  ?  Can  you  find  a  boulder 
with  more  than  one  quartz  vein  through  it  ?  Can  you  find  a 
specimen  with  one  quartz  vein  cutting  another  ?  How  many 
varieties  of  quartz  have  you  now  ? 


EXCITKSIOJST  YIL—  To  the  Field. 
The  Feldspars. 

Now  we  have  made  the  acquaintance  of  one  mineral 
which  is  almost  always  light-colored — sometimes  looking 
almost  exactly  like  glass.  This  quartz  we  find  everywhere. 
It  is  in  almost  all  rocks.  If  we  should  take  one  hundred 
pounds  of  the  average  rocks,  about  sixty  pounds  would  be 
quartz.  When  we  know  quartz  thoroughly  we  are  acquainted 
with  more  than  half  of  all  the  mass  of  the  earth,  so  far  as 
it  is  in  sight. 

But  there  are  other  white  minerals  which  we  found  not 
to  be  quartz.  We  must  study  them  further,  because  we  see 
they  are  very  abundant  also.  Now  we  try  our  steel  on  a  num- 
ber of  them.  Those  which  are  not  scratched  when  we  press 
hard  we  know  to  be  quartz,  and  take  no  further  notice  of 
them.  But  see,  here  is  one  which  we  can  barely  scratch. 


TO   THE   FIELD.  41 

A  piece  of  quartz  will  also  scratch  it.  Probably  we  shall 
find  others  which  scratch  quite  easily;  let  us  pass  these  by 
for  the  present. 

Now  look  at  this  one,  which  we  can  barely  scratch. 
Does  it  look  altogether  like  quartz  ?  Tell  me  how  it  differs 
from  quartz.  Has  it  a  real  glassy  lustre  like  quartz?  Yes, 
you  say ;  but  after  all,  it  is  not  quite  so  glassy.  Turn  it 
until  your  eye  catches  the  light  reflected  from  one  of  its 
surfaces.  It  may  be  a  very  small  surface  ;  but  if  you  can 
catch  the  reflection,  you  will  perceive  that  it  does  not  glisten 
quite  so  brightly  as  a  quartz  surface.  If  you  cannot  get  this 
reflection  from  one  surface,  try  another.  You  need  not 
break  them  out  of  the  rock  to  make  these  trials. 

Next,  tell  me  if  the  form  is  entirely  like  that  of  quartz. 
In  the  first  place  the  real  crystalline  form  of  quartz  can  sel- 
dom be  seen  in  a  rock  mass ;  there  is  no  portion  of  a  hex- 
agonal prism.  Yery  little  of  the  quartz  in  an  ordinary  rock 
shows  that  it  was  broken  from  a  hexagonal  prism.  But 
then,  in  the  second  place,  you  can  find  a  form  in  many 
rocks  which  does  not  belong  to  quartz.  Now  look  carefully 
among  these  whitish  minerals  which  are  not  quartz,  if  we 
may  judge  by  their  hardness.  You  will  see  here  and  there 
some  smooth,  flat  surfaces  like  a  in  Fig.  12.  Well,  quartz  in 
the  rocks  seldom  shows  flat,  smooth  surfaces, 
as  we  just  now  said.  But  look  once  more,  and 
you  will  see  that  some  of  these  smooth,  flat 
surfaces  are  bounded,  on  one  side  at  least,  by 
a  straight  line.  It  is  not  an  irregular  fracture, 
as  if  the  surface  had  been  simply  broken  orf 


GEOLOGICAL   EXCURSIONS. 


there.  You  will  also  perceive  that  this  line  is  the  border 
of  another  surface  which  stands  about  at  right  angles  with 
the  first  surface,  like  two  sides  of  a  box.  In  the  figure,  I  is 
this  other  surface.  You  see  it  is  long  and  narrow.  Sometimes 
you  may  find  it  wide.  Now,  have  you  seen  anything  in 
quartz  like  these  two  surfaces  ?  Not  at  all.  This  is  quite 
another  mineral.  We  call  this  mineral  Feldspar. 

These  are  poor  specimens  of  feldspar ;  but  this  is  the 
condition  in  which  we  generally  find  it,  and  we  must  learn 
to  know  feldspar  as  it  ordinarily  occurs  in  the  rocks.  Yery 
often,  however,  we  meet  with  Oood  specimens,  which  show 
the  form  quite  completely.  If  we  can  find  a  vein  of  whitish 
mineral  in  a  rock  of  some  other  kind,  we  shall  be  likely  to 
get  a  better  view  of  the  crystalline  form,  as  we  call  it. 
Here  is  a  crystal  which  will  enable 
you  to  understand  more  clearly  the 
form  and  lustre  of  feldspar.  The  flat 
surfaces  are  called  faces  or  planes. 
See,  here,  one  plane,  li,  at  right  angles 
with  another,  li.  Also  O  at  right 
angles  with  li.  Who  among  us  has 
the  best  crystal  of  feldspar?  Every 
person  must  keep  the  best  he  has 
until  he  finds  a  better. 

Now,  we  have  talked  about  feldspar 
as  if  it  were  one  kind  of  mineral,  like 
quartz ;  but,  in  truth,  we  have  several 

species  of  feldspar.  Most  commonly  feldspar  has  a  cream  col- 
or or  pinkish  color.  Sometimes  it  is  very  white.  Sometimes 


FIG.  13.  —  LARGE  CRYS- 
TAL OF  ORTHOCLASE, 
A  SPECIES  OF  FELD- 
SPAR. 


TO   THE   FIELD. 


43 


it  is  somewhat  transparent,  like  glass,  and  has  a  more  glassy 
lustre  than  common  feldspar  f  and,  in  this  case,  is  apt  to  be 
composed  of  thin  layers  or  lamellae.  These  are  likely  to  be 
different  feldspars ;  but  we  must  not  try  to  name  different 
species  till  we  have  made  more  advancement.  There  is  an- 
other little  peculiarity  of  certain  feldspars.  Often,  when  the 
light  reflected  from  the  surface  strikes  the  eye,  very  fine 
parallel  lines  or  striae  may  be  seen.  These  generally  indi- 
cate a  feldspar  which  is  not  the  common  species.  Let  us 
look  carefully  for  a  surface  having  these  lines.  Do  not  look 
too  long  in  one  rock.  Try  another.  Sometimes  all  the  feld- 
spar in  one  rock  will  be  of  the  common  kind,  while  in  an- 
other it  will  present  the  striated  surfaces.  In  making  the 
examinations  you  should  have  a  cheap 
pocket  magnifier.  When  you  learn  how 
to  use  it  you  will  find  it  almost  as  indis- 
pensable as  a  pocket  knife.  (See  Fig.  14.) 

If  you  are  unable  to  collect  these  dif- 
ferent species  readily  look  in  some  col- 
lection of  minerals,  and  pick  out  all  the 
quartz  and  all  the  feldspar,  and  point  out 
the  different  feldspars. 

The  most  important  difference  between 
quartz  and  feldspar  we  have  said  nothing 
about,  because  it  does  not  appear  to  the  eye.  Feldspar  is 
made  of  different  elements.  Do  you  remember  what  is 
meant  by  elements  ?  The  chemist  knows  how  to  separate 
feldspar  into  all  its  different  elements,  and  ascertain  how 
much  there  is  of  each  one.  We  are  not  prepared  to  do  this 


FIG.  14.  —  MAGNIFY- 
ING GLASSES. 
a,  OVAL,  b,  BELLOWS- 
SHAPED. 


44  GEOLOGICAL   EXCURSIONS. 

for  ourselves ;  but  we  will  do  it,  if  we  stick  to  the  study. 
Well,  the  chemist  has  ascertained  that  all  feldspars  contain 
silicic  acid,  alumina  and  some  alkali.  Now  the  acid  unites 
with  the  base  alumina,  and  if  the  alkali  were  not  present, 
there  would  be  formed  simply  silicate  of  alumina,  which  is 
also  called  aluminum  silicate.  The  acid  also  unites  with 
the  alkali,  and  if  the  alumina  were  not  present  there  would 
be  formed  simply  a  silicate  of  some  alkali.  But  as  all  are 
present,  there  is  formed  silicate  of  alumina  and  an  alkali. 
Now,  there  are  several  alkalies.  Potash,  soda  and  lime  are 
alkalies.  Either  one  of  these  may  be  the  alkali  in  a  feld- 
spar ;  and  that  is  the  way  we  get  different  species  of  feld- 
spars. So  one  is  a  potash  feldspar  —  and  that  is  the  most 
common  feldspar  (Orthoclase).  Another  is  a  soda  feldspar 
—  and  that  is  generally  white  (Albite).  Another  is  a  lime 
feldspar  —  and  this  is  glassy  and  transparent  (Anorthite). 
Others  are  soda  lime  feldspars ;  and  one  of  these  is  gray, 
brown  or  greenish,  and  sometimes  shows  a  beautiful  play  of 
colors  in  reflected  light  (Labradorite).  Another  (Oligo- 
clase)  is  white,  with  a  faint  greenish  tinge,  and  fine  striae 
on  the  principal  surfaces.  But  you  need  not  learn  all  these 
names  at  present.  All  the  feldspars  mentioned  which  are 
not  orthoclase  may  be  called  Plagioclase. 

Any  feldspar  is  composed  of  silica,  alumina  and  an  alkali. 
The  different  colors  are  caused  by  minute  quantities  of  iron 
and  other  substances.  If  we  take  one  hundred  pounds  of 
common  feldspar,  about  sixty-five  pounds  are  silica,  eighteen 
pounds  alumina,  fifteen  pounds  potash,  about  one  pound 
iron ;  and  the  remaining  pound  is  soda,  magnesia  and  lime. 


TO   THE   FIELD.  45 

When  feldspar  decomposes  it  forms  a  pure  white  clay  called 
Kaolin.  Feldspar  is  used  extensively  in  the  manufacture  of 
porcelain. 

Feldspars  are  very  common  in  crystalline  rocks.  Fine 
specimens  occur  in  St.  Lawrence  and  Orange  counties,  New 
York.  Also  in  Haddam  and  Middletown,  Connecticut;  and 
at  Royalston  and  Barre,  Massachusetts.  Fair  specimens 
may  be  had  in  boulders  all  over  the  northern  states. 

EXERCISES. 

Now,  how  many  specimens  of  quartz  and  feldspar  have  you  ? 
Are  all  your  specimens  of  quartz  different  varieties  ?  Have  you 
a  specimen  of  pink  feldspar?  Have  you  a  specimen  of  pink 
quartz  ?  How  does  the  pink  quartz  differ,  to  your  eyes,  from  the 
pink  feldspar  ?  Have  you  a  specimen  of  cream-colored  feldspar  ? 
What  other  minerals,  so  far  as  you  can  answer,  were  in  the  same 
rock  with  it  ?  Show  me  a  feldspar  with  striations.  Is  it  more 
or  less  glassy  than  one  without  striations  ?  Is  it  orthoclase  or 
a  plagioclase  ?  Can  you  see  the  striations  with  the  naked  eye  ? 
Here  is  a  piece  of  common  feldspar  weighing  one  hundred  grains  ; 
how  many  grains  of  silica  in  it  ?  How  many  grains  of  potash  ? 
What  constituents  of  feldspar  contain  oxygen  ?  What  are  the 
different  elements  in  common  feldspar  ?  Try  and  find  a  piece  of 
dark  feldspar.  Do  all  your  specimens  of  feldspar  show  some  of 
the  peculiar  crystalline  forms  of  the  mineral  ?  Take  your  chem- 
ical cards  and  arrange  them  so  as  to  show  the  composition  of 
common  feldspar.  Also  the  composition  of  other  feldspars. 


46  GEOLOGICAL  EXCURSIONS. 

EXCURSION  VIIL—  To  the  Field. 
Calcite. 

I  wish  you  next  to  make  the  acquaintance  of  another 
light-colored  mineral.  It  is  much  softer  than  feldspar,  and 
you  will  not  be  very  likely  to  find  it  scattered  through  bould- 
ers containing  feldspar  and  dark  minerals.  We  had  better 
look  for  veins  or  seams  of  white  mineral  matter  cutting 
through  other  rocks.  We  shall  probably  find  some  among 
the  boulders.  Ah,  here  is  a  white  vein.  Try  your  steel  on 
it.  Is  it  hard?  Can't  you  scratch  it?  Then  you  know  it 
is  a  quartz  vein.  Besides,  see  how  glassy  it  looks.  We 
may  find  many  quartz  veins.  Here  is  a  soft  vein — very 
much  softer  than  feldspar.  The  steel  scratches  it  very 
easily.  Certainly,  then,  it  is  neither  feldspar  nor  quartz. 
This  is  probably  our  Calcite.  Now  let  us  inspect  it  as  we 
did  feldspar.  Can  you  find  a  smooth  face  anywhere  ? 
There  may  be  plenty  of  them.  Well,  look  at  this  face  or 
flat  surface ;  how  smooth,  shining  and  even  it  looks !  It 
does  not  seem  to  be  a  common  fracture.  How  much  like 
feldspar  it  is !  And  yet  it  is  not  so  pearly  as  feldspar.  Do 
you  see  one  straight  edge  to  this  face  ?  Search  till  you  find 
a  face  which  shows  a  straight  bounding  edge.  Here  it  is. 
The  face  a  is  bounded  by  the  straight  line  m  n. 
Now  you  can  see  that  the  line  shows  where  the 
face  a  is  cut  by  another  plane,  b.  This  is  just  like 
feldspar,  you  say.  Not  quite,  for  you  perceive 
that  these  two  faces  do  not  make  a  right  angle 
with  each  other.  The  angle  is  considerably  more 


TO   THE   FIELD.  47 

or  less  than  a  right  angle.     That  makes  the  plane  angle  at 
m  either  acute  or  obtuse.     How  is  it  in  jour  specimen  ? 

You  can  even  detect  something  further.  A  close  exam- 
ination of  the  face  of  your  crystal  probably  shows  fine  lines 
like  cracks  running  across  or  partly  across.  There  are  two 
sets  of  them.  One  set  runs  exactly  parallel  with  the  side 
m  n,  and  the  other  parallel  with  another  side.  These  are 
cleavage  lines.  The  crystal  breaks  most  easily  along  those 
lines.  Very  likely  you  might  break  out  fragments  which 
would  show  several  faces  —  even  six  faces,  somewhat 
perfect,  all  bounded  by  lines  parallel  on  opposite  sides. 
Here  is  a  fine  large  specimen.  We  often  find  such.  They 

are  generally  rather  opaque ;  but  sometimes 

they  are  clear  as  glass.  You  must  remem- 
ber seeing  such  crystals  on  some  one's 
mantel  or  "  what-not,"  or  in  some  cabinet  FIG.  ie.— CRYSTAL 

OF  CALCITE. 

of  specimens.     You   can  generally   detect 

cleavage  lines  on  the  surfaces  of  these  specimens.     This  is 

calcite. 

But  this  handsome  mineral  often  presents  itself  under 
another  form,  called  dog-tooth  spar,  be- 
cause resembling  somewhat  the  canine 
tooth  of  a  dog.  Here  is  a  figure  of  a 
couple  of  such  crystals  grown  together, 
as  we  generally  find  them. 

This  mineral  is  largely  composed  of 
lime.  It  is  by  far  the  most  important 
lime-containing  mineral.  If  we  take  one 

i-ii  .  r,  i    .,  .    .  FIG.  17.  — DOG-TOOTH 

hundred  grains  of  pure  calcite  it  contains  SPAR. 


48  GEOLOGICAL   EXCUKSIONS. 

forty-four  grains  of  carbonic  acid  and  fifty-six  grains  of 
lime.  It  is  therefore  carbonate  of  lime  —  also  called  cal- 
cium carbonate.  This  is  the  same  composition  as  chalk. 
What  will  be  the  eifect  of  a  little  dilute  acid  applied  ?  It 
should  effervesce  like  chalk.  To  make  sure  of  a  fair  test, 
it  is  better  to  pulverize  the  calcite  and  drop  a  little  acid 
on  it  in  a  test  tube. 

There  are  two  other  minerals  quite  similar  to  this,  differ- 
ing chiefly  in  having  magnesia  in  place  of  all  the  lime 
(which  makes  Magnetite),  or  about  half  of  it  (which  makes 
Dolomite).  But  it  will  not  be  best  to  attempt  to  study  them 
at  present.  They  do  not  effervesce  so  readily  as  calcite.  The 
pulverized  mineral  in  the  test  tube  with  dilute  acid  must  be 
heated  to  produce  active  effervescence. 

Now  you  have  made  the  acquaintance  of  the  three  most 
important  white  or  light-colored  minerals.  If  you  know  them 
well,  and  can  always  distinguish  each  one  from  the  others, 
you  can  make  good  headway  in  naming  rocks  as  soon  as 
you  know  two  or  three  of  the  dark  minerals.  Calcite  you  can 
certainly  distinguish  by  its  comparative  softness.  Feldspar 
can  generally  be  distinguished  by  its  hardness  and  lustrous 
cleavage  faces.  Though  generally  somewhat  glassy,  they 
are  seldom  as  glassy  as  quartz.  After  a  good  deal  of  prac- 
tice you  will  be  able  to  decide  at  a  glance  that  the  feldspar 
is  generally  more  pearly  than  quartz.  In  any  case,  the 
cleavage  planes,  if  you  can  detect  any,  will  decide  the  case. 
Hold  the  specimen  so  that  you  get  reflected  light.  Turn  it 
in  different  positions,  until  the  reflected  light  reveals  a 
cleavage  plane.  The  u glassy  feldspars,"  it  must  be  con- 


TO   THE    FIELD.  49 

fessed,  will  sometimes  trouble  you.  They  look  extremely 
like  quartz  in  lustre,  and  the  crystals  are  often  so  broken  up 
that  it  is  difficult  to  detect  unmistakable  cleavage  planes. 
But  we  must  keep  trying  and  searching.  Yery  seldom  is  it 
really  impossible  to  distinguish  feldspar  from  quartz,  either 
by  lustre,  cleavage  planes,  lines,  angles  or  inferior  hardness. 

EXERCISES. 

Which  of  the  three  white  minerals  contain  silica  ?  What  is 
in  calcite  and  not  in  feldspar  ?  What  is  in  feldspar  and  not  in 
calcite  ?  What  is  in  feldspar  and  not  in  quartz  ?  Suppose  you 
have  a  square  box,  and,  placing  your  hand  on  one  corner,  crush 
it  over  by  pressing  toward  the  opposite  corner  at  the  bottom, 
which  mineral  does  the  box  now  resemble  in  form  ?  How  must 
you  press  the  box  to  produce  the  form  of  one  of  the  other  min- 
erals ?  Did  you  ever  see  a  crystal  of  transparent  calcite  ?  Take 
one  if  you  have  it,  and  lay  it  on  a  printed  line ;  what  is  peculiar 
in  the  appearance  of  the  line  ?  Have  you  found  any  brown  crys- 
tals soft  as  calcite  ?  Have  you  any  brown  crystals  with  curved 
surfaces?  The  brown  crystals  probably  contain  magnesia.  Try 
and  detect  some  intermediate  forms  between  calcite  and  dog- 
tooth spar.  Inquire  among  your  friends  for  specimens  of  crys- 
tals, and  see  what  minerals  they  are.  Of  course  you  can't  name 
them  all  yet.  Please  do  not  neglect  this,  for  we  shall  get  much 
help  in  this  way.  Some  specimens  worth  nothing  where  they 
lie  may  be  exactly  the  things  which  a  student  wants  to  see. 


50  GEOLOGICAL   EXCUKSIONS. 

EXCURSION   IX.— To  the  Field. 
The  Micas,  Hornblende  and  Talc. 

There  are  two  or  three  dark  minerals  of  first  import- 
ance. One  of  these  is  Mica,  although  it  is  not  always 
dark.  Almost  every  one  is  familiar  with  transparent  mica 
as  used  in  our  stoves ;  but  we  will  go  among  the  boulders 
again  for  the  purpose  of  studying  it  as  it  enters  into  the 
formation  of  rocks.  "We  will  seek  a  boulder  with  whitish 
and  dark  varieties  of  minerals  mixed  together.  We  shall 
soon  find  one  in  which  the  dark  mineral  exists  in  small 
thin  scales,  or  piles  of  thin  scales.  That  is  mica.  Some 
people  ignorantly  call  it  isinglass.  Now  select  the  largest 
specimen  at  hand  and  try  with  a  knife-blade  to  separate 
the  thin  leaves.  You  see  there  is  almost  no  limit  to  the 
possible  splitting  of  the  mineral.  If  the  mica  is  bright, 
the  leaves  are  elastic  and  tough.  If  it  is  dull,  the  mica  is 
softer  and  less  elastic.  In  some  rocks  the  mica  is  all  dull. 
In  hardness  mica  is  not  far  from  calcite.  Common  mica  is 
transparent  or  translucent,  and  is  generally  brown,  pale- 
green  or  white.  Deep-black  mica  is  another  species  (Bio- 
tite).  In  New  Hampshire  there  are  plates  of  mica  over  a 
yard  in  diameter. 

Now,  as  to  substances  in  its  constitution,  we  must  say 
that  mica  is  the  name  of  a  family,  as  in  the  case  of  feld- 
spars. But  the  micas  all  contain  silica,  alumina  and  pot- 
ash, and  almost  always  iron.  The  common  mica  (Mus- 
covite) contains  much  iron,  and  that  seems  to  give  it  its 
dark  color.  It  also  contains  magnesia  and  soda.  Water 


TO  THE  FIELD.  51 

is  often  present,  and  that  causes  the  duller  lustre,  lighter 
color  and  less  elastic  leaves  (Hydromica  or  Margarodite). 

Mica  is  a  mineral  which  you  can  hardly  mistake.  Let 
us  examine  next  another  dark  mineral  called  Hornblende. 
It  is  sometimes  green  or  dark  green,  and  frequently  black. 
It  is  exceedingly  common  in  the  boulder  rocks  in  all  the 
northern  states.  It  has  about  the  hardness  of  feldspar, 
and  if  you  scratch  it  the  streak  is  white  or  whitish.  You 
can  generally  detect  a  crystalline  face,  and  sometimes  you 
find  a  crystalline  form  like  a  four-sided  rod.  Sometimes 
the  structure  is  lamellar — that  is,  in  layers  which  are  much 
thicker  than  the  leaves  of  mica,  and  are  not  elastic,  but 
are  apt  to  break  as  you  attempt  to  lift  them  up.  Many 
times,  however,  you  will  not  find  any  crystalline  face. 
The  hornblende  is  simply  a  shapeless 
fragment  closely  imbedded  among  other 
minerals. 

This  is  also  a  silicious  mineral,  and  it 
generally   contains    much   iron,    magnesia,      FIG.  is.— CRYSTALS 

OF  HORNBLENDE. 

alumina,  and  lime.  There  are  many  vari- 
eties, some  of  which  are  white  and  fibrous  (Tremolite, 
Asbestus).  One  variety  (Actinolite)  consists  of  bright- 
green,  radiating  fibres.  There  is  also  another  mineral 
(Augite)  very  similar  to  hornblende,  but  more  inclined 
to  greenish  and  whitish  colors,  and  less  commonly  to 
black  —  though  it  is  sometimes  black.  It  has  cleavage 
surfaces  nearly  at  right  angles  with  each  other.  But  it 
is  difficult  to  distinguish  augite  from  hornblende  by  any 
means  which  we  can  at  present  employ,  though  it  is 


52  GEOLOGICAL  EXCURSIONS. 

very  important  for  the  geologist  to  do  it.  Augite  is 
quite  common. 

There  is  only  one  other  mineral  to  be  troubled  with  in 
this  course  of  study.  That  is  Talc.  It  occurs  often  in 
thin  scales  like  mica,  and  glistens  somewhat.  You  might 
easily  mistake  it  for  mica.  But  let  us  take  a  specimen 
and  pick  apart  the  thin  scales.  See  how  soft  this  mineral 
is.  It  is  the  softest  mineral  in  the  world.  When  you  lift 
up  a  scale  does  it  tend  to  spring  back  on  removing  your 
knife  ?  No,  you  say.  Well,  these  scales  are  not  elastic. 
The  scales  of  mica  are  elastic.  These  are  two  excellent 
ways  for  separating  rnica  and  talc.  Sometimes  they  may 
be  separated  by  the  color,  for  talc  is  pale  and  silvery- 
greenish,  and  never  black.  The  chemist  tells  us,  more- 
over, that  talc  is  a  magnesian  mineral.  It  contains  silica, 
magnesia  and  water.  It  is  a  silicate  of  magnesia. 

Talc  always  feels  smooth  and  greasy.  Eemember  this 
when  you  find  a  specimen  large  enough  to  test  by  the  feel. 
Soapstone  is  nothing  but  talc  all  crushed  and  compacted 
together.  It  is  sometimes  made  into  inkstands  and  grid- 
dles and  foot-warmers.  What  the  well-borers  call  soap- 
stone  is  only  clay  shale  or  indurated  clay. 

EXERCISES. 

Now  let  us  think  over  some  of  the  things  learned.  What  is 
the  name  of  the  glassy  mineral?  What  are  the  white  minerals? 
Are  they  always  white  ?  What  are  the  two  scaly  minerals  ? 
What  minerals  are  sometimes  black?  Which  is  the  softest  of 
the  white  minerals?  Which  is  most  glassy?  Which  is  the  softest 
of  the  black  minerals  ?  Which  mineral  effervesces  when  acid  is 


TO   THE   FIELD. 


53 


applied  ?  Why  does  not  hornblende  effervesce?  Which  ones 
of  all  these  minerals  will  scratch  calcite?  Which  will  calcite 
scratch  ?  Which  cannot  be  scratched  by  any  of  the  others  ? 
Which  minerals  contain  silica?  Which  contain  iron?  Which 
calcium  ?  Which  magnesium  ?  Which  aluminum  ?  What 
other  chemical  elements  exist  in  any  of  these  minerals?  Which 
ones  are  most  easily  detected  by  their  crystalline  form  ?  Which 
by  its  hardness?  Which  by  its  softness?  Have  you  ever  seen 
the  crystalline  form  of  mica  in  any  rock  ?  What  minerals  are 
often  green  or  greenish  ?  Which  minerals  sometimes  occur 
black  and  sometimes  white?  Which  one  is  sometimes  shaped 
like  needles?  Which  like  fine  silk  fibres?  What  minerals  are 
likely  to  be  kinkish  ?  What  ones  of  a  cream  color  ?  Which 
ones  will  scratch  glass?  Which  cleave  most  readily?  Which 
least  readily  ? 

Here  is  a  table  showing  the  composition  of  all  these  minerals. 
Their  names  will  be  seen  at  the  head  of  the  columns,  and  the 
names  of  the  various  substances  which  combine  together  to  form 
the  minerals  are  at  the  left.  In  the  case  of  feldspar  we  have 
considered  simply  common  feldspar  (Orthoclase),  with  its  most 
common  composition.  The  same  is  true  of  mica  and  hornblende. 
The  figures  show  how  many  pounds  or  grains  of  each  element  are 
present  in  100  pounds  or  grains  of  the  mineral. 


Quartz. 

Feldspar. 

Mica. 

Horn- 
blende. 

Talc. 

Calcite. 

Silica, 

100 

65 

45 

47 

62 

Alumina, 

18 

32 

12 

Alkali,     . 

15 

10 

Magnesia, 

.  . 

15 

31 

Lime, 

1 

11 

56 

Iron  Oxide,    . 

1 

5 

12 

2 

Carbonic  Acid,    . 

44 

Water, 

4 

4 

Other  Substances, 

1 

3 

3 

1 

•• 

100 

100 

100 

100 

100 

100 

54  GEOLOGICAL  EXCURSIONS. 

EXCUKSION   X.—  Among  the  Moulders. 
Quartzose  Hocks. 

Let  us  continue  our  wanderings  among  the  boulders. 
We  are  ready  now  to  learn  the  names  of  some  of  the 
commonest  rocks.  The  rocks  are  composed  of  mixtures 
of  minerals,  or,  in  a  few  cases,  of  single  minerals.  The 
majority  of  all  the  rocks  are  formed  from  the  six  common 
minerals  which  we  have  studied.  This  seems  surprising ; 
but  we  must  remember  that  each  mineral  may  present 
many  variations  in  color,  and  that  feldspar  and  mica  exist 
each  in  several  species.  Then,  again,  the  same  minerals 
may  exist  in  different  proportions  in  different  rocks,  and 
the  minerals  may  be  in  different  conditions  as  to  fineness 
and  as  to  crystallization.  Also,  rocks  having  the  same 
mineral  ingredients  may  differ  in  structure.  All  these 
things  we  will  now  proceed  to  see  for  ourselves. 

One  of  the  very  commonest  of  rocks  in  all  the  northern 
states  and  among  the  pebbles  of  the  southern  states  is 
composed  of  a  single  mineral,  and  that  mineral  is  quartz. 
The  name  of  the  rock  is  Quartzite  ;  but  there  are  almost 
endless  varieties  of  it.  Let  us  find  a  white  boulder  nearly 
uniform  in  color.  Here  it  is.  Test  it  for  hardness.  Is 
it  as  hard  as  quartz  ?  If  not,  we  will  pass  it  by.  If  this 
white  rock  is  as  hard  as  quartz,  then  it  is  one  variety  of 
quartzite.  The  farmers  would  say  it  is  a  " flint  rock,"  or 
a  "hard  head."  Now  look  closely  at  it.  Yery  probably 
you  will  notice  some  variation  in  color  in  different  parts. 
Probably,  also,  you  can  discover  an  obscure  bounding  line 


AMONG  THE   BOULDERS.  55 

to  the  differently  colored  parts.  If,  however,  the  bound- 
ing lines  are  indistinct,  and  the  whole  rock  breaks  through 
like  glass,  this  is  a  vitreous  quartzite.  Some  vitreous 
quartzites  show  quite  striking  contrasts  of  color  in  dif- 
ferent parts.  These  are  apt  to  be  coarse  or  conglomeritic. 
Let  us  find  a  vitreous  quartzite  which  is  jaspery. 

In  many  quartzites  the  different  parts,  whether  of  dif- 
ferent colors  or  not,  are  clearly  so  many  different  pebbles 
or  cobble-stones.  The  rock  seems  to  be  a  mass  of  rounded 
quartz  stones  cemented  together.  This  is  a  quartzose 
conglomerate.  There  are  also,  sometimes,  conglomerates 
composed  of  rounded  stones  which  are  not  quartzose, 
Also,  many  conglomerates  have  the  different  stones  feebly 
cemented  together.  But  here  we  come  on  something  dif- 
ferent. It  is  a  quartzite  composed,  evidently,  of  grains  of 
sand,  for  we  can  see  the  outlines  of  separate  grains 
throughout.  Well,  this  is  a  granular  quartzite. 

Now  suppose  the  granular  quartzite  to  be  a  little  less 
firmly  cemented.  It  is  simply  a  coarse  sandstone  or  grit. 
When  you  break  this  sort  of  rock  you  do  not  notice  the 
glassy  lustre  of  the  quartzites.  The  grindstone  is  a  sand- 
stone. The  "Nova  Scotia  stone"  so  much  admired  for 
building  purposes  is  a  sandstone,  and  so  is  the  u  brown 
stone  "  used  so  extensively  for  fine  buildings  in  New  York 
and  other  eastern  cities.  It  is  found  in  great  abundance 
along  the  valley  of  the  Connecticut  River  and  in  northern 
New  Jersey.  Throughout  the  states  of  New  York  and 
Pennsylvania  are  many  reddish,  yellowish  and  grayish 
sandstones.  In  Ohio  are  many  quarries  of  beautiful  build- 


56  GEOLOGICAL   EXCURSIONS. 

ing  stones  known  as  "Waverly  sandstone.  The  sandstones 
and  grindstones  from  Berea  and  Cleveland  are  mostly  of 
a  grayish  and  bluish  color,  and  much  admired  for  window 
sills  and  caps.  In  Michigan  very  similar  stone  is  quarried 
at  Point  aux  Barques  on  Lake  Huron.  In  the  southern 
part  of  the  state  the  same  stone  is  often  quite  reddish. 
In  Ottawa  county  it  is  bluish.  In  Iowa,  at  Burlington  and 
in  that  neighborhood,  it  is  yellowish.  Other  kinds  of 
sandstones  are  always  likely  to  be  found  in  the  vicinity  of 
beds  of  coal.  Often  they  have  black  charcoal-like  specks 
in  them.  Sandstones  are  liable  to  contain  various  impu- 
rities, consisting  most  frequently  of  lime  or  clayey  matter 
or  iron-oxide.  Many  sandstones  have  minute  mica-scales 
scattered  through  them.  These  are  micaceous  sandstones. 

EXERCISES. 

It  is  time  to  get  together  all  our  specimens  of  quartzose 
rocks.  There  are  endless  varieties,  although  only  one  of  our  six 
common  minerals  has  been  employed  in  their  formation.  Please 
pick  out  the  specimens  which  you  think  might  be  called  quartz- 
ites.  Are  all  the  rest  sandstones?  What  is  the  difference 
between  a  sandstone  and  a  quartzite  ?  Are  both  quartzose  ? 
Are  both  silicious  ?  Have  you  any  granular  quartzites  ?  Sepa- 
rate them  from  the  others.  What  kind  of  quartzites  are  the 
others?  What  is  the  most  compact  variety  of  quartzose  rocks? 
Show  me  a  jaspery  quartzite  if  you  have  it.  Show  me  a  quartz- 
ite with  dark  flints  in  it.  Have  you  noticed  any  mica-scales  in 
any  quartzite?  What  other  minerals  have  you  seen  in  any  of 
your  quartzites?  Is  there  any  feldspar  or  hornblende?  Have 
you  seen  any  quartzite  with  black  straight  crystals  running 
through  it;  and  are  they  hornblende?  Are  the  sides  curved 
and  unevenly  striated  ?  If  so,  they  may  be  Tourmaline.  Have 


AMONG   THE   BOULDERS.  57 

you  found  any  pure  quartz  running  through  a  rock  which  was 
not  all  quartz  ?  If  so,  there  was  a  vein  of  quartz.  Have  you 
found  any  calcite  in  contact  with  quartz?  Was  it  in  a  quartz- 
ite  ?  Do  you  discover  any  talc  scales  in  any  quartzite  ?  What 
is  the  difference  between  a  granular  quartzite  and  a  gritty  sand- 
stone ?  What  sort  of  rock  is  a  whetstone  ?  What  is  an  oil 
stone  ?  What  is  a  hone  ?  Is  there  anything  peculiar  about  a 
scythe  stone  ?  Examine  a  piece  of  sandstone  with  your  magni- 
fier and  see  if  you  can  clearly  perceive  the  grains  of  quartz.  Is 
the  quartz  clear  or  colored  ?  Do  you  see  anything  except  grains 
of  quartz  ?  What  seems  to  hold  the  grains  together  ?  What  is 
the  color  of  the  other  material  ?  Put  a  drop  of  your  acid  on  the 
sandstone;  does  the  rock  effervesce?  If  not,  what  do  you  con- 
clude the  other  material  to  be  ?  If  it  does,  what  is  indicated  ? 
Would  carbonate  of  lime  hold  the  quartz  grains  together?  Now 
try  and  make  a  sandstone  yourself.  Put  some  loose,  clean,  fine 
sand  in  a  small  box  and  pour  some  lime  water  on  it,  allowing  it 
to  leach  through  slowly.  Then,  after  an  hour  or  two,  pour  on  a 
little  more.  Repeat  this  a  number  of  times,  and  then  allow  the 
sand  to  dry,  and  see  if  the  grains  are  cemented  together.  Try 
this  experiment  at  home  and  report  success  when  we  meet  for 
next  excursion.  Bring  your  sandstones  with  you. 


EXCURSION  XL— Among  the  Boulders. 
Micaceous  Rocks. 

We  stick  to  the  boulders,  and  I  will  tell  you  why.  It  is 
because  boulders  are  found  almost  everywhere,  so  that  a 
person  in  any  part  of  our  northern  states  can  easily  find 
specimens  of  rocks.  Another  reason  equally  good  is  that 
these  boulders  are  of  so  many  different  kinds  that  almost 
everywhere  may  be  had  all  the  principal  sorts  of  rocks.  In 
many  places  rocks  which  are  not  boulders  may  be  found,  and 


58  GEOLOGICAL  EXCURSIONS. 

we  will  examine  them  by  and  by;  but  not  at  present,  because 
most  students  do  not  live  near  quarries  and  ledges  of  rocks. 
Besides  that,  we  can  only  find  one  sort  of  rock  at  a  quarry 
or  a  ledge,  generally  speaking,  while  the  boulders  in  one 
field  will  furnish  ten  or  twenty  sorts  of  rocks. 

Well,  how  did  you  succeed  with  your  experiment  ?  Did 
you  make  any  sandstone?  Now,  that  is  one  way  in  which 
nature  sticks  together  grains  and  crystals  to  make  rocks. 
But  take  this  rock  with  mica-scales  in  it  and  apply  acid.  It 
does  not  effervesce ;  so  there  is  no  calcium  carbonate  in  it. 
But  the  parts  are  well  stuck  together;  how  is  it  done?  Ex- 
amine with  the  lens;  do  you  see  any  kind  of  cement? 
There  is  nothing  of  this  kind  visible  —  and  yet  how  firm  the 
rock  is.  We  must  keep  this  question  in  mind,  as  we  con- 
tinue our  studies. 

You  see  mica  in  this  rock;  what  other  minerals  do  you 
find  ?  You  say  quartz,  certainly ;  that  is  right.  Mica  and 
quartz  have  great  fondness  for  each  other,  and  are  very 
generally  found  in  company.  But  they  have  a  mutual  friend, 
feldspar,  which  seems  to  be  equally  intimate  with  both  mica 
and  quartz.  Ah,  you  say  feldspar  is  here  too  ?  Very  likely, 
as  I  said.  Well,  now  tell  all  about  the  appearance  of  this 
feldspar.  How  do  you  know  it  is  not  calcite?  How  do  you 
know  it  is  not  another  variety  of  quartz?  Are  you  quite 
sure  we  have  in  this  rock  the  three  minerals,  quartz,  feldspar 
and  mica?  Is  there  no  other  mineral  present?  Only  a  very 
little  of  something,  you  say,  in  one  corner  of  the  specimen. 
Well,  no  matter  for  that.  But  are  these  three  minerals 
evenly  distributed  through  the  specimen,  or  is  the  mica 


THE   BOULDEBS.  59 

more  abundant  in  certain  streaks  across  the  rock?  Ob,  you 
say  the  mica  is  arranged  in  streaks.  Yes,  the  quartz,  too, 
is  not  quite  evenly  distributed.  This,  then,  is  a  stratified 
rock.  Let  us  lay  it  aside,  and  take  another  specimen  not 
stratified.  There,  this  is  entirely  unstratified.  But  look 
closely  and  be  sure  that  it  contains  quartz,  feldspar  and  mica. 
Does  it?  And  is  there  no  other  mineral  somewhat  plentiful 
in  it?  Well,  this  rock  is  what  we  call  granite.  Now  think 
this  over  and  state  what  a  granite  is.  Granite  is  a  most 
important  rock.  You  have  accomplished  much  when  you 
can  be  sure  whether  any  rock  is  a  granite  or  not.  Many 
other  rocks  are  called  granite  by  quarrymen  and  stone  cut- 
ters ;  but  you  must  judge  for  yourself. 

Take  notice.     It  makes  no  difference  whether  the  granite 
is  coarse  or  fine;  it  is  still  granite.     A  fine  granite  may  be 
better  for  building  purposes 
than     a     very    coarse    one. 
Sometimes    quartz,    feldspar 
and  mica  are  thrown  together 
in  so  coarse  a  state  that  the 

granite  is  worth  nothing  as  a  Fia.lo. -PORPHYRITIC  ROCK. 

building    stone.       A    granite  Granite  from  Land's  End,  Eng- 

land.    (Lyell.) 

with  large    crystals  of  feld- 
spar scattered  through  it,  is  called  a  porphyritic  granite. 
Any  rock  with  such  feldspar  crystals  is  called  porphyritic. 

Take  notice  again.  It  makes  no  difference  what  is  the 
color  of  the  quartz,  or  what  is  the  color  of  the  feldspar,  or 
what  is  the  color  of  the  mica.  "Well,  how  many  possible 
variations  there  must  be  in  the  appearance  of  granites!  In 


60  GEOLOGICAL   EXCURSION'S. 

some,  the  reddish  spots  are  quartz ;  in  others,  the  reddish 
spots  are  feldspar.  Sometimes,  also,  there  are  two  kinds  of 
quartz.  Sometimes  there  are  two  kinds  of  feldspar.  Some- 
times there  are  two  kinds  of  mica.  A  good  way  for  us  is  to 
go  to  a  stone  cutter's  and  examine  different  sorts  of  granites. 

Take  notice  the  third  time.  Some  granites  contain  but 
little  mica,  and  then  the  rock  may  be  very  light-colored. 
But,  if  either  the  quartz  or  feldspar  is  reddish,  the  rock  will 
be  variegated  whitish  and  reddish.  In  some  granites,  on 
the  contrary,  the  mica  is  exceedingly  abundant.  If  the  mica 
is  black  it  gives  a  dark  complexion  to  the  rock.  So  the 
number  of  varieties  of  granite  is  almost  endless.  In  some 
cases  there  is  almost  no  mica,  and  the  rock  is  then  a  Gran- 
ulite.  If  mica  and  quartz  are  both  wanting,  or  nearly  so, 
the  rock  is  a  Felsite.  In  some  felsites,  quartz  is  intimately 
combined  with  feldspar.  This  forms  a  Petrosilex  if  the 
feldspar  is  orthoclase,  and  a  proper  Felsite  if  the  feldspar 
is  a  plagioclase.  Granite  blocks  are  often  used  for  street 
paving. 

You  remember  that  all  the  granites  are  unstratified.  We 
had  at  first  a  rock  with  the  constituents  of  granite,  but  we 
found  it  stratified,  and  laid  it  aside.  Here  it  is.  Such  a 
rock  we  call  Gneiss  (pronounced  Gn-ice,  not  Gne-iss).  Of 
course  now,  there  may  be  just  as  many  varieties  of  gneiss  as 
of  granite.  Some  varieties  are  so  little  stratified  that  one 
would  take  them  for  granites  unless  we  had  large  samples 
to  examine.  Such  gneisses  always  pass  for  granites  among 
stone-cutters.  Many  of  them  are  quite  as  valuable  as  gran- 
ites for  building  purposes. 


AMOKG  THE   BOULDEKS.  61 

But  here  is  a  micaceous  rock  which  is  very  distinctly 
stratified.  See  how  abundant  is  the  mica.  It  is  arranged 
in  courses  of  varying  thickness,  and  between  the  courses  is  — 
what?  Well,  it  is  mostly  quartz  in  grains.  In  one  speci- 
men it  is  wholly  quartz ;  in  another  we  can  detect  a  little 
feldspar.  Kow,  such  a  rock  we  call  Mica  Schist  (pronounced 
Shist).  A  schist  is  any  rock  composed  of  beds  or  layers  of 
crystalline  minerals.  There  are  many  sorts  of  schists,  as 
we  shall  see.  Perhaps  if  we  look  around,  we  shall  discover 
a  mica  schist  with  garnets  in  it.  Every  one  knows  garnets. 
We  will  keep  this  question  in  mind.  If  the  mica  is  soft  and 
lustreless  we  have  a  Hydromica  Schist.  We  shall  certainly 
meet  with  such.  Mica  schists  are  much  used  for  sidewalks. 

Occasionally  we  find  an  unstratified,  granite-like  rock 
consisting  of  quartz  and  mica.  This  is  called  Greisen  (pro- 
nounced Gri-sen).  But  a  little  mica  in  a  common  quartzite 
would  make  a  micaceous  quartzite. 

We  must  not  forget  about  these  important  rocks. 

EXERCISES. 

Give  the  names  of  the  micaceous  rocks.  Which  ones  are 
stratified?  Which  is  most  distinctly  stratified?  Suppose  a 
fragment  of  rock  is  handed  you  and  you  find  it  unstratified  and 
containing  quartz,  feldspar  and  mica,  what  is  its  name  ?  But  then 
suppose  another  fragment  from  the  same  boulder  or  ledge  is 
stratified;  what  is  the  name  of  that  fragment?  Then  would  you 
say  one  part  of  a  boulder  or  ledge  is  granite  and  another  part  of 
the  same  is  gneiss  ?  Just  exercise  your  best  judgment  in  giving 
the  answer,  for  many  questions  cannot  be  answered  positively. 
Suppose  the  part  of  a  ledge  which  seems  to  be  gneiss  ten  rods 
away  from  the  part  which  seems  to  be  granite,  must  we  call  it  all 


62  GEOLOGICAL   EXCURSIONS. 

granite  or  all  gneiss  ?  Suppose  you  find  a  granite  boulder  or  a 
ledge  with  a  vein  of  quartz  running  through  it,  does  that  make 
the  ledge  or  boulder  gneiss?  Suppose  a  vein  of  feldspar 
runs  through  it,  what  kind  of  rock  forms  the  ledge?  Sup- 
pose a  vein  is  composed  of  quartz  and  feldspar  intermixed, 
what  kind  of  rock  is  the  vein  ?  Does  that  prevent  the  ledge  from 
being  granite  ?  Well,  suppose  the  vein  is  of  quartz,  feldspar  and 
mica,  what  kind  of  rock  is  the  vein  ?  Does  that  make  the  ledge 
stratified  ?  May  we  have  two  sorts  of  granite  in  one  ledge  or 
boulder  ?  Please  find  a  granite  in  which  the  feldspar  is  glassy. 
Can  you  find  one  with  a  dusky  feldspar  ?  Have  you  found  a  por- 
phyritic  granite  ?  Suppose  we  could  remove  the  mica  from  a 
granite,  what  would  the  rock  become  ?  Suppose  we  find  a  granu- 
lite  stratified,  what  should  we  call  it  ?  Suppose  we  could  remove 
the  feldspar  from  a  granite,  what  would  the  rock  become  ?  Did 
you  ever  see  such  a  rock  ?  Did  you  ever  see  a  rock  composed  of 
mica  alone  ?  Did  you  ever  see  a  rock  composed  of  feldspar 
alone  ?  Ask  your  father  or  some  other  person  to  tell  you  the 
composition  of  granite.  Ask  some  one  to  tell  you  the  difference 
between  granite  and  gneiss.  If  any  person  asks  you  such  ques- 
tions, do  not  fail  to  answer  them  satisfactorily. 

Now  let  us  hear  about  your  success  in  making  a  sandstone. 
Show  the  sandstones  made.  Is  such  a  sandstone  different  from 
old  mortar  ?  Now  explain  how  it  is  that  mortar  becomes  so  hard. 
What  would  be  the  effect  if  much  dirt  were  mixed  with  the  sand 
used? 


EXCUKSION  XII.—  With  the  Stone  Cutter. 
Hornblendic  Rocks, 

For  the  sake  of  varying  our  excursions  a  little  we  will 
visit  the  stone  cutter's  yard,  where  many  varieties  of  rocks 
may  be  found,  such  as  are  used  for  building  and  for  ceme- 
tery monuments.  In  some  parts  of  the  West,  churches  and 


WITH   THE   STOJs'E   CUTTEK.  63 

residences  are  constructed  of  rough-dressed  boulders.  The 
boulders  are  hauled  from  the  neighboring  fields  and  ravines, 
and  workmen,  with  heavy  sledge  hammers,  break  them  into 
suitable  shapes  for  putting  into  the  walls  of  a  building. 
Cart  loads  of  freshly  broken  chips  are  made,  and  the  vari- 
eties of  rocks  which  may  be  picked  up  are  almost  endless  in 
number.  If  all  that  carting  and  hammering  had  been  done 
expressly  for  the  geologist,  it  could  not  have  been  better 
done.  Such  a  place  is  even  better  than  a  stone  cutter's 
yard  ;  and  we  will  visit  it  afterward. 

Here  at  the  stone  cutter's.  You  see  rocks  white,  clouded, 
reddish,  red-mottled  and  red-specked,  gray,  black  and  white 
variegated,  black  and  red  variegated,  and  other  sorts.  Now, 
to-day  we  wish  to  study  hornblendic  rocks.  We  must  look 
for  rocks  containing  hornblende.  "What  is  the  prevailing 
color  of  hornblende  ?  Well,  pick  out  your  hornblendic 
rock.  Here  it  is  ;  what  other  minerals  do  you  find  in  it  ? 
Quartz  and  feldspar,  you  say.  That  is  a  very  common  sort 
of  mixture.  Here  you  have  the  same  two  minerals  in  com- 
pany which  you  found  in  granite.  But  the  mutual  friend  is 
not  mica.  It  is  hornblende  in  this  case.  Such  a  mixture  is 
not  granite,  whatever  the  stone  cutter  may  tell  you.  It  is 
Syenite.  Bear  that  name  in  mind.  It  is  the  same  kind  of 
rock  as  the  ancient  Egyptians  quarried  at  Syene,  in  Egypt, 
and  the  geologists  thought  it  would  be  pleasant  to  name  the 
rock  from  the  place.  But  it  is  wonderful  that  the  Syene 
rock  should  be  found  in  all  parts  of  the  world. 

Notice  how  much  syenite  resembles  granite.  Even  some 
scientific  writers  include  it  in  granite.  We  may  also  have 


64  GEOLOGICAL  EXCURSIONS. 

numerous  varieties  corresponding  to  the  varieties  of  granite. 
Often  the  feldspar  is  reddish,  and  then  we  have  the  so-called 
" Scotch  granite."  Some  of  these  syenites  are  fine,  some 
are  coarser.  Some  have  a  dark  complexion  and  some  a 
light  one.  Most  of  the  so-called  granites  from  Maine  to 
Massachusetts  are  syenite.  The  Quincy  granite,  which  is 
sent  to  New  York  and  the  southern  states  and  the  West 
Indies,  is  a  syenite.  The  custom  house  and  other  buildings 
in  "Wall  street,  New  York,  are  of  syenite.  The  capitol  at 
Albany  is  chiefly  syenite.  There  is  a  large  amount  of  syen- 
ite in  the  Upper  Peninsula  of  Michigan  ;  also  in  northern 
Wisconsin  and  Minnesota.  Syenite  is  even  more  durable 
than  granite.  Syenite  and  granite  are  both  found  in  enor- 
mous ledges  and  mountain  masses  along  the  eastern  flanks 
of  the  Alleghanies  to  North  Carolina.  In  Ohio  you  will 
only  find  syenite  and  granite  in  the  form  of  boulders.  The 
same  is  true  of  the  Lower  Peninsula  of  Michigan,  of  Indi- 
ana and  Illinois. 

It  often  happens  that  some  mica  is  present  in  syenite, 
and  then  we  have  a  micaceous  syenite.  If  the  mica  is  nearly 
as  abundant  as  the  hornblende  we  have  a  syenitic  granite. 
If  the  mica  is  much  more  abundant  than  the  hornblende, 
the  rock  is  a  granite,  but  it  is  hornblendic.  Let  us  look 
around  and  find  some  of  these  species  of  rocks  in  the  stone 
yard. 

We  shall  have  to  go  back  to  our  boulders,  after  all,  to 
get  all  the  sorts  of  hornblendic  rocks.  Now  here  is  a  syen- 
ite-looking rock,  but  it  contains  almost  no  quartz  ;  what 
shall  we  call  it?  Well,  if  the  feldspar  is  common  feldspar, 


WITH   THE   STONE   CUTTEE.  65 

the  rock  is  Hyposyenite  —  which  some  say  is  the  only  proper 
syenite.  Is  the  feldspar  reddish  or  creamy?  Then  it  is 
common  feldspar  or  orthoclase.  But  is  the  feldspar  pure 
white  ?  Then  it  is  probably  albite.  Now,  hornblende  and 
albite  form  a  rock  called  Diorite.  This  is  a  handsome  rock, 
with  its  white  and  black  or  greenish  colors.  Sometimes 
diorite  is  coarse  enough  to  enable  us  to  study  the  minerals  ; 
but  sometimes  it  is  very  fine,  If  any  other  light-colored 
feldspar  not  orthoclase  is  mixed  with  hornblende,  we  call 
the  rock  diorite  also.  Diorite  is  a  very  tough  rock,  and 
makes  a  building  stone  of  the  first  class.  Diorites  are  very 
common  about  Lake  Superior.  Also  among  the  boulders  of 
all  the  northern  states. 

If  the  dark  mineral  in  a  diorite-looking  rock  is  not  horn- 
blende, but  augite,  then  the  rock  is  Diabase.  So  diabase  is 
a  rock  composed  of  augite  and  a  feldspar  not  of  the  ortho- 
clase group  —  that  is  augite  and  a plagioclase.  Some  main- 
tain recently  that  most  of  our  northwestern  rocks  heretofore 
called  diorites  are  in  reality  diabases.  But  this  is  not  certain. 

All  these  hornblendic  rocks  are  unstratified  ;  but,  as  with 
the  micaceous  rocks,  we  have  many  gneissic  forms.  Syenite 
stratified  is  syenitic  gneiss.  Diorite  stratified  is  dioritio 
gneiss.  Diabase  stratified  is  diabasic  gneiss.  If  the  feld- 
spar in  a  syenite  is  supposed  diminished  and  the  hornblende 
increased,  and  the  rock  is  distinctly  stratified,  we  get  a 
hornblende  schist.  This  corresponds  to  mica  schist.  If  the 
quartz  is  supposed  removed  from  a  hornblende  schist,  little 
besides  hornblende  remains,  and  we  have  hornblende  rock. 
This  is  a  black  rock,  and  by  no  means  uncommon.  It  is, 


66  GEOLOGICAL   EXCURSIONS. 

however,  schistose,  and  has  some  lustre.  Many  black  and 
lustreless  rocks,  not  showing  distinct  crystals,  contain  other 
minerals  besides  hornblende.  They  are  then  simply  horn- 
blendic.  Sometimes  a  dark  feldspar  (Labradorite)  is  abun- 
dant in  such  rocks.  But  we  must  not  undertake  to  study 
this  group  of  rocks  at  present.  We  will  confine  ourselves 
to  rocks  in  which  the  crystals  are  visible  to  the  naked  eye, 
or,  at  least,  with  a  magnifier.  Such  rocks  are  called  phanero- 
crystalline ;  and  those  in  which  you  cannot  distinguish  sepa- 
*  rate  crystals  are  called  cryptocrystalline.  These  are  pretty 
long  words,  but  they  are  no  stranger  than  you  can  find  by 
the  dozen  in  any  fashion  book. 

Take  notice.  In  both  the  micaceous  and  the  hornblendic 
series  of  rocks,  we  have  mixtures  of  minerals  which  may  be 
unstratified,  or  may  be  obscurely  stratified,  or  may  be  very 
distinctly  stratified.  Now  let  us  call  the  first  kind  massive, 
the  second  gneissoid,  and  the  third  schistose. 

Just  as  we  have  micaceous  and  hornblendic  rocks,  so  we 
may  have  a  series  of  talcose  rocks.  Quartz,  feldspar  and 
talc,  when  massive,  give  us  Protogine ;  when  gneissoid, 
protogine  gneiss ;  when  schistose,  talcose  schist,  since,  in  the 
latter  case,  very  little  feldspar  is  ever  found.  When  a  schist 
consists  almost  wholly  of  talc,  it  is  a  talc  rock /  and  if  the 
talc  is  pulverized  and  closely  packed,  the  rock  is  steatite. 

EXERCISES. 

Now  let  us  review  again.  Sit  down  by  your  collection  of 
rocks  and  pick  out  all  the  hornblendic  specimens.  Next  sort  out 
those  which  are  true  syenites.  Lay  aside  the  hyposyenite.  Pick 
out  the  diorites.  Arrange  the  syenites  according  to  their  coarse- 


WITH   THE   STOJJE   CUTTER.  67 

ness.  Now  arrange  all  the  massive  hornblendic  rocks  according 
to  the  amount  of  quartz  in  them.  Next  arrange  the  gneissoid 
and  schistose  rocks  of  the  hornblendic  series  according  to  the 
amount  of  quartz  in  them.  Suppose  the  hornblende  in  all  these 
schistose  rocks  should  change  to  mica,  what  would  their  several 
names  become?  Suppose  it  should  change  to  talc,  what  would 
the  names  become  ?  Take  a  specimen  of  syenite  in  hand  and 
suppose  the  hornblende  to  change  to  mica,  what  does  the  rock 
become  ?  Suppose  the  hornblende  to  change  to  feldspar,  what  is 
the  name  of  the  rock?  But  if  you  hold  syenite  and  the  quartz 
changes  to  feldspar,  what  is  the  rock?  If  the  quartz  changes  to 
hornblende,  what  is  the  rock  ?  Now,  if  you  take  hyposyenite, 
what  kind  of  feldspar  is  in  it?  If  the  orthoclase  changes  to 
albite,  what  does  the  rock  become?  What,  if  it  changes  to 
oligoclase?  If  you  take  hyposyenite  and  add  mica,  what  might 
we  call  the  rock?  If  we  add  talc  instead,  then  what?  What 
sort  of  rock  is  the  glistening  scythe  stone  ?  Which  is  the  tough- 
est rock,  diorite  or  granulite  ?  Look  on  the  weathered  surface  of 
a  granitic  or  a  syenitic  boulder,  and  state  what  mineral  projects 
most.  Which  has  changed  its  color  most?  Which  weathers 
most  rapidly,  hornblende  or  feldspar?  What  change  in  lustre 
does  feldspar  undergo  in  weathering  ? 

You  must  be  very  particular  to  see  for  yourselves  all  the 
things  about  which  these  questions  are  asked.  When  you  go 
home  tell  your  people  what  hyposyenite  is,  and  ask  them  to 
explain  diorite. 

REVIEW. 

Here  is  a  table  to  assist  the  memory  and  to  aid  in  review. 
The  minerals  studied  are  placed  at  the  top  of  the  columns.  At 
the  side  also  are  placed  the  minerals,  as  well  as  the  names  of 
rocks  formed  of  two  minerals;  as  also  syenite.  Then  the  names 
of  rocks  formed  by  uniting  minerals  and  rocks  named  at  side  and 
top  are  found  in  the  spaces  where  the  vertical  and  horizontal  col- 
umns intersect.  Rocks  whose  names  are  printed  in  small  capitals 
are  massive  ;  those  whose  names  are  in  ordinary  letters  are  gneiss- 


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GRANULITE. 
Granulitic  Gneiss. 
Granulitic  Schist. 

ALBITIC  GRANTJLITE 
Granulitic  Schist. 

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Granulitic  Schist. 

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TO   THE   MARBLE   YARD.  69 

old,  and  those  whose  names  are  in  italics  are  schistose.  Some  of 
the  unfilled  spaces  might  receive  the  names  of  rocks  not  men- 
tioned ;  but  it  is  best  not  to  be  troubled  with  rare  rocks.  Also 
the  spaces  at  the  upper  right  hand,  containing  stars,  might  be 
filled  with  the  same  names  as  are  in  other  parts  of  the  table. 
The  pupil  may  exercise  himself  in  doing  it. 


EXCURSION  XIII.— To  the  Marble  Yard. 

Calcareous  Rocks. 

You  must  have  noticed  that  none  of  the  rocks  which  we 
have  studied  thus  far  contain  any  calcite.  It  might  be  that 
calcite  crystals  should  occur  sparingly  in  some  of  these  rocks, 
but  they  are  not  essential.  If  they  should  so  occur  we 
might  describe  the  rock  as  calciferous.  But  when  a  rock  is 
composed  chiefly  of  calcite  we  call  it  calcareous.  There  are 
many  such  rocks. 

Here  we  are  in  the  marble  yard.  Nearly  all  marbles  are 
calcareous.  The  stone  cutter  has  many  varieties  of  marbles. 
Pick  up  some  of  these  marble  chips  and  test  them  for  hard- 
ness. They  are  all  rather  soft.  Test  some  of  them  with 
acid.  They  all  effervesce.  If  you  find  a  rock  having  the 
hardness  of  marble,  which  does  not  effervesce,  it  is  probably 
formed  of  dolomite  instead  of  calcite — or  at  least,  in  part  of 
dolomite.  Pulverize  a  bit,  put  the  powder  in  a  test  tube, 
pour  in  a  little  dilute  acid  and  heat  the  tube.  Now  you 
perceive  effervescence.  Yes,  this  is  also  a  carbonate,  and  the 
acid  with  heat  (if  not  without)  drives  off  the  gaseous  car- 
bonic acid. 

You  will  notice  that  some  of  these  marbles  are  coarse. 


70  GEOLOGICAL   EXCURSIONS. 

If  you  look  closely  you  will  perceive  plenty  of  crystalline 
faces.  It  looks  as  if  a  quantity  of  calcite  crystals  had  been 
broken  and  compacted  together.  The  so-called  Potomac 
marble  is  of  this  kind.  It  has  been  used  in  building  the 
Washington  monument.  It  is  too  coarse  for  fine  work. 
Here  is  a  granular  marble,  white  like  loaf  sugar,  and  having 
the  texture  of  loaf  sugar.  Such  marbles  are  called  sacchar- 
oidal.  Here,  next,  is  a  finer  marble.  It  only  differs  from 
the  last  in  fineness.  The  finest  marbles  may  be  used  for 
making  statues.  For  this  reason  they  are  called  statuary 
'marbles. 

Some  marbles  are  colored  in  various  ways,  and  thus  we 
get  almost  countless  varieties  of  them.  Many  Vermont 
marbles  are  clouded  and  veined  with  a  darker  color  than  the 
ground  color.  The  ground  color  itself  is  sometimes  far  from 
white,  inclining  to  a  bluish  or  clay  color.  Some  marbles  are 
reddish.  The  red  color  is  either  uniform  or  distributed  in 
blotches,  clouds  or  veins.  There  are  some  varieties  with 
much  dark  matter  as  a  ground  color,  or  forming  veins. 
Egyptian  marble,  so  called,  is  almost  black,  with  occasional 
veins  of  a  lighter  color.  All  the  colorings  of  marbles  are 
produced  by  impurities.  Reddish  colors  are  often  caused 
by  iron  oxide  closely  combined  with  the  calcite.  Blackish 
colors  are  commonly  due  to  carbon  or  bitumen  disseminated 
through  the  rock.  Bluish  veinings  and  ground  colors  seem 
to  be  caused  by  argillaceous  (clayey)  materials. 

Some  fine  varieties  of  marble  are  produced  by  the  com- 
bination of  distinct  bodies.  One  of  the  Tennessee  marbles 
is  a  conglomerate  or  pudding  stone.  This  is  a  favorite  mar- 


TO   THE   MARBLE   YARD.  71 

ble  for  pillars  of  public  buildings.  Sometimes  a  compact, 
calcareous  rock  has  numerous  forms  of  corals,  shells  and 
other  things  distributed  through  it,  and  if  it  takes  a  fine 
polish,  it  forms  what  is  called  shell  marble. 

Light-colored  and  clouded  marbles  of  various  kinds  are 
quarried  at  various  localities  from  northern  New  England  to 
Maryland.  Western  Vermont,  Massachusetts  and  Connec- 
ticut, and  also  eastern  New  York,  abound  in  marble  ledges. 
Black  marble  is  quarried  at  Shoreham,  Vt.,  and  also  near 
Lake  Champlain.  Yerd-antique  marble  occurs  at  Milford, 
Ct.,  and  also  in  Essex  county,  N.  Y.  This  is  common 
marble  clouded  green  with  serpentine.  Shell  marbles  are 
found  in  Onondaga  and  Madison  counties,  ~N.  Y.  "White 
saccharoidal  marbles,  sometimes  fine  enough  for  statuary, 
are  found  extensively  in  the  regions  south  of  Lake  Superior. 
All  over  New  England  and  the  northwestern  states  may 
be  found  boulders  of  marble. 

We  are  still  in  the  marble  yard.  You  notice  that  the  fine 
cemetery  marbles  are  supported  by  bases  of  some  sort  of 
rock  not  marble.  This  is  probably  a  calcareous  rock.  Try 
your  acid  on  it.  Does  it  effervesce  ?  Well,  it  is  a  limestone 
not  crystalline  enough  to  take  a  fine  polish.  Still,  it  is  com- 
posed mostly  of  calcite.  You  see  it  is  distinctly  stratified; 
the  marbles  are  not  so.  There  are  many  varieties  of  lime- 
stone ;  but  there  are  three  characters  by  which  you  may  dis- 
tinguish them  from  most  other  rocks.  1.  They  effervesce 
with  acids.  2.  They  are  easily  scratched.  3.  They  are  not 
composed  of  worn  or  rounded  grains.  There  is  a  variety 
made  up  largely  of  uniform  spherical  pellets  stuck  together 


72  GEOLOGICAL  EXCURSIONS. 

by  a  fine  cement,  or  sometimes  imbedded  in  it,  but  these  are 
not  grains  rounded  by  wearing.  It  is  called  oolitic  limestone. 
Limestones  may  contain  various  impurities — silica,  clay, 
sand,  iron,  coal,  bitumen,  petroleum  and  still  other  sub- 
stan^es.  So  we  describe  the  limestone  as  silicious,  argil- 
laceous, arenaceous,  ferruginous,  carbonaceous,  bituminous 
or  petroliferous. 

What  is  chalk?  That  we  found  to  be  capable  of  effer- 
vescing. It  is  simply  a  soft  limestone.  There  are  all  grades 
of  limestones  in  point  of  hardness,  between  marbles  and 
chalk.  The  carbonate  of  lime  precipitated  in  the  bottom  of 
a  little  lake  is  marl.  It  is  often  mixed  with  clay  or  peat. 
We  can  frequently  find  marl  beneath  the  peat  of  a  common 
swamp.  The  carbonate  of  lime  precipitated  from  flowing 
spring  water  is  travertin  and  calcareous  tufa,  as  before  ex- 
plained. That  which  forms  in  the  shape  of  icicles  hanging 
from  the  roofs  of  caves  is  stalactite.  When  the  same  water 
falls  on  the  floor  of  a  cave  and  makes  a  deposit,  we  call  it 
stalagmite.  This  is  exactly  like  travertin. 

When  limestone  is  burned,  the  carbonic-acid  gas  is  driven 
off  and  only  lime  remains.  If  lime  is  left  exposed  to  the 
air,  especially  if  damp  or  wet,  it  takes  carbonic  acid  again 
from  the  air  and  water,  and  is  reconverted  into  carbonate  of 
lime. 

EXERCISES. 

Did  you  ever  notice  the  crust  formed  around  stones  in  the 
bottom  of  a  brook  ?  What  is  it  ?  Where  does  it  come  from  ? 
How  may  stones  or  grains  of  sand  become  cemented  together  ? 
What  is  the  stone  base  of  your  oil  lamp  ?  Why  is  marble  used 


TO   THE   MARBLE   YARD.  73 

instead  of  quartzite  ?  How  many  sorts  of  marbles  have  you 
collected  ?  Arrange  them  in  order  according  to  their  coarseness. 
How  many  sorts  of  limestones  have  you  ?  Arrange  them  accord- 
ing to  their  hardness.  How  does  chalk  differ  from  marble? 
What  is  the  difference  between  stalactite  and  stalagmite  ?  Does 
a  stalactite  increase  internally  or  externally  ?  Does  other  lime- 
stone grow  ?  Which  is  most  compact,  marble  or  quartzite  ? 
What  causes  the  surfaces  of  marbles  long  exposed  to  the  weather 
to  turn  black  ?  Can  limestone  be  dissolved  in  water  ?  What 
other  rocks  or  minerals  thus  far  studied  can  also  be  dissolved  ? 
Do  the  rains  dissolve  limestones  ?  What  effect  have  limestones 
on  the  soil?  Are  limestone  soils  desirable  for  farming  purposes? 
Are  sandy  soils  equally  desirable  ?  Why  not  ?  Have  you  ever 
seen  a  black  marble  or  limestone  ?  What  causes  rusty  stains  on 
the  surfaces  of  some  white  marbles  ?  Which  are  best  stratified, 
marbles  or  common  limestones  ?  Suppose  you  find  a  limestone 
with  fine  sand  distributed  through  it,  what  is  the  name  of  the 
rock  ?  What  is  the  taste  of  lime  ?  Is  lime  soluble  or  insoluble  ? 
When  limewater  is  exposed  to  the  air,  what  causes  the  film  which 
forms  on  the  surface  ?  How  does  this  differ  from  limestone  ? 
Were  limestones  formed  in  this  way  ?  Take  an  oyster  shell  and 
test  it  with  acid  ;  does  it  effervesce  ?  Now  burn  the  shell  and 
see  if  it  becomes  lime.  Of  course  you  will  postpone  this  until 
you  have  a  convenient  fire.  But  suppose  the  shell  burned,  you 
will  see  that  it  has  the  acrid  taste  of  lime.  Could  mortar  be 
made  of  it  ?  Take  any  other  shell  and  test  it  in  the  same  way. 
Suppose  a  common  river  clam  shell  (properly  called  Uhio)  should 
lie  in  the  water  until  the  shell  disintegrates,  what  would  the 
powder  be  ?  Suppose  thousands  of  shells  should  disintegrate  in 
the  same  way,  what  would  be  found  on  the  bottom  of  the  pond  ? 
Is  this  the  way  marl  is  made  ?  Suppose  calcareous  spring  water 
should  flow  into  the  pond,  would  anything  be  precipitated  ? 
What?  How  would  this  differ  from  marl?  Now  which  way 
does  marl  originate  ?  Which  would  you  think  most  durable  for 
building  purposes,  marble  or  granite  ?  What  causes  the  parallel 


74  GEOLOGICAL   EXCUKSIONS. 

lines  in  a  piece  of  polished  stalagmite  ?  Have  you  found  any 
fragments  of  a  brown  or  blackish  limestone?  If  so,  rub  it 
smartly  with  another  stone  and  see  whether  any  odor  is  emitted  ? 
What  variety  of  limestone  is  this  ?  Have  you  found  limestones 
with  hard  flinty  patches  forming  what  is  called  cherty  limestone  ? 


EXCUKSION  XIV.—  To  the  Clay  Pit  and  the  Field. 
Argillaceous  Bocks. 

Let  us  begin  to-day  with  this  broken  slate.  It  has  been 
used  in  school  for  writing  on,  and  is  called  graphic  slate. 
Do  you  see  any  indications  of  quartz  or  calcite  in  it  3  How 
many  sorts  of  minerals  does  it  seem  to  be  composed  of? 
All  one  kind,  you  say.  Try  it  with  your  magnifier.  Can 
you  see  any  crystals  or  grains  ?  Not  at  all.  It  is  very  dif- 
ferent from  the  granites  and  schists.  Try  your  acid  on  it. 
No  effervescence ;  it  is  not  a  carbonate.  Let  us  put  a  frag- 
ment in  a  mortar  and  reduce  it  to  fine  powder.  There,  that 
is  done.  Now  moisten  the  powder  a  little,  and  what  does 
your  slate  look  like  ?  Like  mud,  you  say.  So  it  is  mud. 

Were  you  ever  in  a  brick  yard,  or  in  a  clay  pit  where 
material  is  obtained  and  ground  up  for  bricks  ?  Well,  does 
the  clay  make  you  think  of  your  pulverized  slate  ?  They  are 
in  fact  both  the  same.  The  brick  clay  probably  has  some 
very  fine  silicious  sand  disseminated  through  it.  You  might 
dissolve  the  clay  in  water  and  allow  the  fine  sand  to  settle 
to  the  bottom,  as  it  did  in  the  case  of  the  garden  soil.  The 
remainder  would  be  almost  exactly  like  this  pulverized 
slate.  I  must  tell  you  what  is  the  mineral  in  these  sub- 


TO   THE   CLAY   PIT   AND   THE   FIELD.  75 

stances  which  gives  them  their  character  ;  it  is  alumina. 
But  this  is  rather  a  chemical  substance  than  a  mineral.  But 
the  aluminous  substances  are  not  formed  of  any  distinct 
minerals,  as  quartzite  and  marble  are.  The  alumina  enters 
directly  into  the  formation  of  rocks. 

Did  you  ever  notice  in  the  coal  bin  an  occasional  flat 
piece  of  stone  called  u  slate"?  You  can  almost  always  find 
some  "slate  "  among  the  coal.  Here  is  a  piece  ;  try  it  with 
your  steel.  Do  you  find  it  as  hard  as  the  graphic  slate  ?  It 
is  softer,  you  say.  Well,  pulverize  a  piece,  and  see  whether 
it  makes  a  similar  kind  of  mud.  It  does.  Now,  is  there 
no  way  to  distinguish  this  from  the  graphic  slate  ?  It  is 
rough,  but  that  is  only  because  it  is  in  a  state  of  nature.  It 
is  softer,  you  say.  But  there  is  no  other  difference.  It  is 
an  aluminous  rock,  but  is  softer  than  real  slate.  We  call 
such  a  rock  shale. 

If  we  stroll  among  the  boulders  again,  we  shall  see  some 
blackish,  fine-grained  rocks  which  we  never  yet  ventured  to 
take  in  hand.  Do  they  seem  to  be  hornblende  rocks?  No, 
they  have  not  sufficient  lustre.  Are  they  black  marble  ? 
No,  they  are  too  hard.  It  is  difficult  to  scratch  them. 
Notice  the  fine,  even  lines  of  stratification ;  do  they  resem- 
ble a  hornblende  rock  or  hornblende  schist  ?  Not  at  all ; 
this  is  a  kind  of  rock  not  yet  studied  by  us.  I  must  tell  you 
the  name.  It  is  argillite.  It  is  composed  of  alumina  and 
silica  closely  mixed.  It  is  true  that  hornblende  is  also 
present  with  some  argillites,  and  so  are  minute  scales  of 
mica.  It  is  also  true  that  some  very  fine  hornblendic  rocks 
resemble  this.  But  the  argillite  is  the  rock  with  which  we 


76  GEOLOGICAL   EXCUKSIOtfS. 

are   concerned.      Examine   it   carefully.      This   is   also   an 
aluminous  rock. 

Thus  we  have  a  series  of  aluminous  rocks  ranging  from 
argillite,  which  is  almost  flinty,  to  clay,  which  can  be 
moulded  in  the  hand.  The  purest  sort  of  clay  is  Kaolin. 
It  is  nearly  white,  and  we  often  find  it  in  association  with 
quartz  and  mica,  in  such  a  situation  as  to  show  that  Kaolin 
is  simply  decomposed  feldspar.  The  alkali  has  been  dis- 
solved out  of  the  feldspar,  and  some  of  the  silica  has  disap- 
peared. What  remains  is  nearly  pure  alumina  and  water. 
So  we  see  how  the  decomposition  of  granite  or  other  rocks 
containing  feldspar  has  given  origin  to  the  vast  beds  of 
impure  blue  clay  used  for  bricks,  pottery,  tiles  and  other 
purposes.  The  pure  Kaolin  is  used  for  porcelain.  Even 
feldspar  is  often  ground  up  for  the  same  purposes.  The 
alkali  in  it  gives  the  ware  a  translucent,  glassy  character. 

EXERCISES. 

Suppose,  in  the  decomposition  of  feldspar,  the  alkali  is  not  all 
removed,  and  the  clay  resulting  is  burned,  what  will  be  the 
appearance  of  the  bricks?  What  causes  the  red  color  of  common 
bricks  ?  Why  are  some  bricks  not  red  ?  What  is  the  peculi- 
arity of  Milwaukee  bricks?  Can  you  name  another  locality 
which  affords  light-colored  bricks  ?  Why  is  porcelain  whiter 
than  common  bricks?  What  is  the  cause  of  the  translucency 
of  China  ware  ?  Did  you  ever  observe  statuettes  of  biscuit, 
or  unglazed  porcelain,  to  be  called  "  Parian  marble  "  ?  Are  they 
of  any  kind  of  marble?  Do  the  sellers  seem  to  think  they  are 
real  marble  ?  How  do  they  differ  from  marble  ?  What  is  the 
difference  between  graphic  slate  and  roofing  slate  ?  What  are 
slate  pencils  made  of  ?  Are  slates  and  pencils  ever  made  of  any 
other  than  an  aluminous  rock  ?  What  sort  of  slate  pencils  could 


TO   THE   CLAY   PIT   AND   THE   FIELD. 


77 


be  made  of  steatite?  What  is  the  "French  chalk"  used  by 
tailors?  Do  all  clays  belong  to  the  Drift?  What  are  the  colors 
of  the  slates  which  you  have  seen?  How  are  letters  and  designs 
sometimes  represented  upon  slated  roofs?  Of  what  are  the  tiles 
made  which  are  used  on  floors  and  about  fireplaces?  What  use 
do  sculptors  and  modellers  make  of  clay  ?  When  did  mankind 
begin  to  use  clay  for  pottery?  Why  are  not  silicious  argillites 
employed  for  roofing?  How  does  argillite  differ  from  Egyptian 
marble  ? 

REVIEW. 

Now  let  us  recall  some  of  our  lessons.  We  have  had  a  series 
of  silicious  rocks  and  a  series  of  calcareous  rocks,  and  here  is  a 
series  of  aluminous  rocks.  Each  series  begins  with  rocks  which 
are  hard  and  not  well  stratified,  and  ends  with  rocks  which  are 
incoherent  or  soft.  It  will  aid  our  memory  to  get  these  arranged 
in  order  in  a  table.  Here  is  such  a  table: 


TABLE  OF  ARRANGEMENT  OF  FRAGMENTAL  ROCKS. 


GROUPS  or 
ROCKS. 

CRYSTALLINE. 

INDURATED. 

SEMI- 
INDURATED. 

INCOHERENT. 

SILICIOUS 
ROCKS. 

Quartzite  — 
Vitreous. 
Granular. 
Conglomeritic. 

Sandstone  — 
Compact. 
Conglomerate. 

Sandstone  — 
Friable. 

Sand. 

ALUMINOUS 
ROCKS. 

Argillite. 

Slate. 

Shale. 

Kaolin. 
Clay. 

CALCAREOUS 
ROCKS. 

Marble  — 
Conglomeritic. 
Saccharoidal. 
Statuary. 

Limestone  — 
Compact. 
Travertin. 
Calcareous  Tufa. 

Limestone  — 
Soft. 
Chalk. 

Marl. 

This  is  a  table  of  rocks  which  do  not  occur  very  extensively 
as  boulders.  Leaving  out  the  "crystalline"  "silicious  rocks," 
those  which  remain  are  not  sufficiently  hard  to  endure  the  usage 
to  which  boulders  have  been  subjected.  Yet,  leaving  boulders 
out  of  the  account,  the  most  abundant  bed  rocks  throughout  the 
country  are  those  designated  above  as  "indurated"  and  "semi- 
indurated."  That  is,  outside  of  New  England  and  a  region 


78  GEOLOGICAL   EXCUKSIOKS. 

along  the  eastern  flanks  of  the  Alleghanies,  the  common  bed 
rocks  of  the  country  are  of  the  indurated  and  semi-indurated 
sorts,  until  we  are  north  of  Albany,  Lake  Huron  and  Minneapo- 
lis. But  the  boulder-forming  rocks  furnish  us  with  a  much 
greater  number  of  varieties  than  these  fragmental  rocks.  It  is 
in  the  fragmental  rocks  that  we  find  fossil  shells  and  corals. 
These  things  are  of  intense  interest  for  study,  but  we  cannot  take 
them  up  until  we  reach  a  more  advanced  course. 

Very  often  we  find  silicious  matter  mixed  with  aluminous  and 
calcareous  rocks;  also  aluminous  matter  mixed  with  silicious  and 
calcareous  rocks;  also  calcareous  matter  mixed  with  silicious  and 
aluminous  rocks.  Then  we  have  to  prefix  the  qualifying  word 
"silicious,"  "aluminous"  or  "calcareous"  to  the  proper  name  of 
the  rock.  So  we  may  have  silicious  slates  or  limestones;  alum- 
inous sandstones  or  limestones,  and  calcareous  sandstones  or 
shales.  Further,  if  iron  oxide  imparts  its  reddish  or  yellowish 
color  to  any  of  these  rocks  they  are  also  ferruginous.  In  the 
same  way  any  of  these  rocks  may  be  bituminous,  carbonaceous, 
micaceous  or  petroliferous. 


EXCURSION  XV.— To  the  Specimen  Drawers. 
Exercises  in  Identifications. 

"We  may  arrange  an  analytical  table  to  enable  us  to 
determine  the  commoner  rocks.  This  will  also  present  the 
subject  in  another  light.  There  is  nothing  in  the  table 
which  has  not  been  included  in  the  previous  lessons.  It  is 
only  requisite  that  the  pupil  should  be  able  to  identify  the 
principal  minerals,  and  understand  the  terms  which  have 
been  already  explained. 

Now,  let  us  take  any  specimen  at  random,  and  see  if  we 
can  ascertain  its  name  by  the  use  of  this  table.  Then  we 
will  try  other  specimens. 


TO   THE   SPECIMEN    DKAWEES.  79 


ANALYTICAL  TABLE  FOR  THE  DETERMINATION  OF  THE 
COMMONEST  ROCKS. 

A.   Crystalline,  some  of  the  constituent  minerals  having  shining,  lustrous 

surfaces,  or  fine,  compact,  and  hard. 
I.   Phanerocrystalline,  consisting  of  minerals  distinguishable  with  naked 

eye  or  pocket  lens. 
1.   No  effervescence  with  acids. 

(1)  Quartz  present  and  no  other  mineral,  Quartzite. 

(2)  Feldspar  alone  with  quartz. 

(a)  Structure  massive,  Granulite. 

(b)  Structure  schistose,  Granulitic  Schist. 

(3)  Mica  present  in  thin,  glistening,  elastic  scales. 

(a)  Quartz  present,  and  no  third  mineral. 

(aa)  Structure  thick-bedded,  Micaceous  Quartzite. 

(bb)  Structure  thin-bedded,  Mica  Schist. 

(b)  Quartz  and  feldspar  present  with  the  mica. 

(aa)   Structure  massive,  Granite. 

(bb)  Structure  thick-bedded  Gneiss. 

(cc)  Structure  thin-bedded,  little  feldspar,        Mica  Schist. 

(4)  Hydromica  present  in  thin,  lustreless,  inelastic  scales. 

(a)  Quartz  present,  and  no  third  mineral. 

(aa)  Structure  thick-bedded,  Hydromica  Quartzite. 

(bb)  Structure  thin-bedded,  Hydromica  Schist. 

(b)  Quartz  and  feldspar  present  with  the  hydromica. 

(aa)  Structure  massive,  Hydromica  Granite. 

(bb)   Structure  thick-bedded,  Hydromica  Gneiss. 

(cc)  Structure  thin-bedded,  Hydromica  Schist. 

(5)  Hornblende  present. 

(a)  No  mineral  but  hornblende,  Hornblende  Mock. 

(b)  Quartz  present  and  no  third  mineral. 

(aa)  Structure  thick-bedded,  Horriblendic  Quartzite. 

(bb)  Structure  thin-bedded,  Hornblende  Schist. 

(c)  Quartz  and  feldspar,  with  hornblende. 

(aa)  Structure  massive,  Syenite. 

(bb)  Structure  thick-bedded,  Syenitic  Gneiss. 

(cc)  Structure  thin-bedded,  little  feldspar, 

Hornblende  Schist. 

(d)  Orthoclase  only  with  the  hornblende,  structure  massive, 

Hyposyenite. 


80  GEOLOGICAL   EXCUKSIONS. 

(e)  Plagioclase  only  with  the  hornblende. 

(aa)  Structure  massive,  Diorite. 

(bb)  Structure  schistose,  Diorite  Schist. 

(6)  Augite  present. 

(a)  No  mineral  but  augite,  Augite  Rock. 

(b)  Quartz  only,  or  chiefly,  with  augite,  Augite  Schist. 

(c)  Plagioclase  only  with  augite. 

(aa)   Structure  massive,  Diabase. 

(bb)  Structure  schistose,  Diabase  Schist. 

(d)  Orthoclase  only  with  augite,  Augite  Hyposyenite. 

(7)  Talc  present. 

(a)  No  mineral  but  talc,  |  ™^^' 

(b)  Talc  alone  with  quartz. 

(aa)   Structure  thick-bedded,  Talcose  Quartzite. 

(bb)  Structure  thin-bedded,  Talcose  Schist. 

(c)  Talc  and  orthoclase  with  quartz. 

(aa)   Structure  massive,  Protogine. 

(bb)  Structure  thick-bedded,  Protogine  Gneiss. 

(cc)  Structure  thin-bedded,  Protogine  Schist. 

2.   Effervescence  with  acids,  Marble. 

II.    Cryptocrystalline,  constituent  minerals  undistinguishable. 
(Determinations  uncertain  by  simple  inspection.) 

1.  Hardness  equal  to  quartz,  lustre  glassy,  Vitreous  Quartzite. 

2.  Hardness  a  little  less  than  quartz,  lustre  dull. 

(1)  Color  black  [sometimes  Diorite  or  Diabase,  but 

frequently],  Aphanite. 

(2)  Color  very  dark,  structure  generally  banded,  Silicious  Argillite. 

(3)  Color  reddish,  whitish,  greenish,  smoky,  lustre  horny,   Felsite. 
B.   Uncrystalline  (fragmental),  distinctly  stratified. 

I.  Effervescence  with  acids,  at  least  when  heated. 

1.  Rock  hard,  often  containing  fossils,  Limestone. 

2.  Rock  easily  cut  with  a  knife,  Chalk. 

3.  Rock  without  much  coherence,  Marl. 

II.  No  effervescence  with  acids,  or  only  very  little. 

1.  No  quartzose  grains. 

(1)  Rock  can  be  cut  with  a  knife,  Slate. 

(2)  Rock  very  easily  cut,  Shale. 

2.  Quartzose  grains  present. 

(1)  Grains  cohering  together,  Sandstone. 

(2)  Materials  uncemented,  Sand. 


BY   THE    WATEKSIDE.  81 

Do  not  think  all  rocks  can  be  determined  by  this  little 
table.  If  you  try  a  specimen  which  can  not  be  so  deter- 
mined, lay  it  aside  until  you  have  opportunity  to  take  a 
more  thorough  course. 

If  you  can  use  this  table,  and  determine  the  more  com- 
mon rocks,  you  certainly  have  made  an  excellent  start. 
You  already  know  something  about  geology.  Should  you 
go  no  farther,  you  will  have  much  satisfaction  in  under- 
standing something  about  the  most  common  rocks  all  over 
the  northern  United  States. 


EXCUKSION  "XN\.—By  the  Waterside. 

Sediments. 

How  often  we  have  noticed  a  sediment  in  some  standing 
liquid.  This  little  observation  is  the  key  to  the  geological 
work  which  has  made  nearly  all  the  rocks  known  to  us. 
Let  us  go  out  and  study  some  sediments  recently  made  by 
geological  action.  We  hardly  step  into  the  street  without 
noticing  some  deposits  left  by  the  last  shower.  We  walk 
along  a  country  road  and  soon  find  a  spot  where  the  torrent 
of  water  has  reached  the  level  ground  and  laid  down  its 
load  of  sand  and  stones  brought  from  the  hill  slope.  See 
the  method  of  assortment.  First,  the  coarse  stones  were 
dropped  as  soon  as  the  force  of  the  water  was  slackened  too 
much  to  bear  them  along.  Then,  after  a  little  further 
slackening,  smaller  stones  were  dropped.  Just  beyond 
these  we  find  small  pebbles  and  sand ;  and  the  fine  mud  has 
accumulated  in  the  hollow  where  the  water  stood.  Why  are 
there  no  pebbles  at  the  bottom  of  the  roadside  puddle  ? 


82  GEOLOGICAL   EXCURSIONS. 

And  why  is  there  no  mud  at  the  foot  of  the  hill  where  the 
cobble  stones  lie? 

If  we  go  down  to  the  brook  side  in  the  meadow,  we  shall 
find  a  low,  flat  place  which  the  stream  overflows  occasion- 
ally. A  little  examination  will  show  that  the  soil  here  is 
simply  a  brook  or  river  sediment.  It  is  alluvium,  formed 
from  the  deposit  of  the  stream.  There  is  drift  material  in 
it,  composed  of  stems  and  chips  and  bits  of  lumber,  besides 
leaves  and  grasses.  There  are  also  some  whitened  shells 
which  once  lived  in  the  stream. 

Let  us  go  down  by  the  pond.  Do  you  notice  the  steep 
banks  around  one  or  two  sides  and  the  low,  marshy  margin 
on  another  side  ?  See  how  the  rushes  and  the  cat  tails  rise 
from  the  shallow,  stagnant  water  near  the  shore.  See  the 
sedges  and  grasses  growing  in  the  bog  nearer  the  shore. 
These  plants  are  killed  by  every  winter's  frosts,  and  the  old 
stems  fall  down  and  go  to  decay  almost  exactly  in  the  places 
where  they  grew.  They  decompose  into  a  blackish  sort  of 
soil  called  peat.  How  thick  a  deposit  of  peat  do  you  sup- 
pose might  be  accumulated  in  a  man's  lifetime  ?  Would  it 
not  pretty  nearly  fill  the  pond,  especially  on  the  side  where 
the  vegetation  grows  so  rankly  ?  Now  this  query  leads  us 
to  look  a  little  farther  back  from  the  shore.  Here  is  quite  a 
broad,  marshy  belt  (see  Figure  20),  and  beyond  is  some 
meadow  land.  All  this  marsh  and  meadow  land  is  as  level 
as  the  pond  or  lake.  Still  beyond,  the  dry  upland  begins. 
Now  it  looks  exactly  as  if  the  lakelet  had  once  extended  to 
the  upland,  and  had  become  filled  with  peat  as  far  as  the 
level  surface  extends.  Let  us  go  and  dig  in  the  meadow 


BY   THE    WATERSIDE. 


83 


FIG.  20. —  THE  LAKELET  SLOWLY  FILLING. 
FORMATION  OF  MARL  AND  PEAT. 

and  see  if  it  is  peat.  Certainly  it  is.  It  is  true,  then,  that 
the  lakelet  is  filling,  and  is  made  shorter  every  year  on  the 
side  where  the  vegetation  grows  so  luxuriantly.  But  does 
the  filling  and  shortening  take  place  only  on  one  side  ?  Let 
us  think  a  minute.  Which  way  do  the  winds  blow  mostly? 
Why,  they  blow  from  the  side  opposite  the  marsh.  Then 
all  the  leaves  and  twigs  and  grasses  which  get  into  the 
water  are  blown  over  toward  the  marshy  side.  Certainly ; 
and  when  the  lakelet  first  existed  these  drifted  materials 
were  lodged  at  the  foot  of  the  slope  on  that  side,  and  went 
to  decay  and  formed  a  sort  of  peaty  material  in  the  bottom 
of  the  water.  After  some  years  the  deposit  became  con- 
siderably extended.  Meantime  the  plants  which  like  to 
grow  in  stagnant,  shallow  water  made  their  appearance 
there ;  and  nothing  else  has  been  necessary  but  to  let  these 
operations  have  time  enough,  and  the  whole  breadth  of  the 
peaty  marsh  would  grow  into  existence  just  as  we  see  it. 
That  is  the  explanation  of  the  marsh  and  meadow  on  one 
side  of  the  lakelet.  Of  course,  much  dirt  has  washed  down 
the  hill  slopes  on  the  other  sides  and  has  gone  into  the 


84  GEOLOGICAL   EXCURSIONS. 

lakelet.  The  coarser  material  has  been  left  near  the  shore, 
and  the  finer  has  been  floated  into  the  deeper  water.  Some 
has  floated  over  to  the  marsh  side,  and  the  fine  aluminous 
mud  has  settled  down  and  mingled  with  the  growing  peat. 

Now,  you  ask  if  this  pond  or  lakelet  will  not  become 
completely  filled  by  and  by.  Of  course  it  will.  There  are 
plenty  of  lakelets  which  have  been  filled  already.  How  do 
you  suppose  the  place  would  look  if  the  pond  had  been  quite 
filled  already  ?  Why,  that  level  meadow  would  extend  all 
over  it.  There  would  be  no  more  lakelet.  There  would  be 
a  level  marsh.  Well,  don't  you  know  any  level  marsh 
exactly  such  as  you  think  this  pond  will  become  by  and  by  ? 
Of  course,  you  know  a  good  many  of  them.  One  is  all 
overgrown  with  flags  and  rushes,  and  one  is  full  of  tamarac 
trees,  and  another  has  alder  bushes  growing  all  over  it.  If 
you  ask  your  father  or  your  uncle,  or  some  other  man  who 
has  lived  here  a  good  many  years,  he  will  tell  you  he 
remembers  when  the  water  stood  in  the  place  where  that 
bog  is.  He  may  remember  when  the  dam  was  built,  and  the 
mill  pond  formed  —  when  the  water  first  overflowed  some  of 
the  land.  He  will  tell  you  that  the  water  at  first  was  clear, 
but  now  you  can  see  that  the  mill  pond  is  half  grown  up 
with  rushes,  and  is  filling  every  year. 

Now  you  are  asking  about  that  white  substance  which 
was  dug  from  under  the  peat  in  a  certain  place.  I  will  tell 
you  about  it.  Come  with  me  to  the  water.  In  most  ponds 
and  lakelets  you  may  find  some  little  shells  —  some  uni- 
valves like  snails,  and  some  bivalves  like  clams.  They  form 
their  shells  from  the  calcium  carbonate  in  the  water ;  and 


BY   THE   WATERSIDE.  85 

the  calcium  carbonate  comes  from  the  limestone  in  the  soil 
or  rocks  through  which  the  water  flows  which  tills  the  lake- 
let. This  is  not  abundant  in  New  England,  but  it  is  through- 
out the  West.  When  the  animal  in  the  shell  dies,  the  shell 
rests  on  the  bottom  and  slowly  decomposes.  In  time  it 
forms  over  the  bottom  a  bed  of  white,  soft,  calcareous  mat- 
ter called  marl.  So,  as  the  peat  bed  extends,  it  forms  above 
the  bed  of  marl ;  and  after  the  water  is  quite  displaced 
by  these  accumulations,  we  find  a  bed  of  peat  underlaid  by 
a  bed  of  marl.  These  marl  beds  are  most  abundant 
in  the  western  states ;  but  peat  beds  form  wherever  there 
are  lakelets  and  vegetation.  The  bed  of  peat  maybe  called 
a  stratum  of  peat;  and  the  bed  of  marl  a  stratum  of  marl. 
So  you  see  what  is  the  origin  of  these  two  strata. 

In  spring,  after  the  heavy  rains,  the  streams  are  full  of 
sediment.  Even  a  summer  shower  will  muddy  all  the  small 
streams.  Where  do  these  sediments  go?  The  stream 
empties  into  another  stream  or  into  a  lake,  or  into  the  ocean. 
But  wherever  the  stream  empties,  the  water  gets  finally  into 
the  sea,  and  some  of  the  sediment  is  compelled  to  go  with 
it.  When  the  sediments  reach  the  sea  they  may  be  tossed 
about  for  a  time  by  the  waves,  but  they  must  finally  settle 
to  the  bottom.  The  water  of  the  Mississippi  River  is  full 
of  mud  at  all  times  of  the  year.  Immense  quantities  are 
brought  down  by  the  Missouri  River.  When  you  travel  on 
a  Mississippi  River  steamboat,  they  will  fill  your  drinking 
glass  with  water  from  the  muddy  river.  One  accustomed  to 
the  clear  water  of  the  eastern  and  northern  states  can  hardly 
endure  such  drinking  water.  Let  a  glass  of  it  stand  for 


86  GEOLOGICAL    EXCURSIONS. 

thirty  minutes  and  a  frightful  amount  of  mud  settles  to  the 
bottom.  Well,  where  does  all  this  mud  in  the  Mississippi 
go  ?  Into  the  gulf  of  Mexico  necessarily  —  except  what  set- 
tles upon  the  land  at  times  of  overflow.  The  sediment 
carried  into  the  gulf  is  literally  filling  it  up.  Some  of  the 
finest  floats  a  long  time  and  settles  to  the  bottom  hundreds 
of  miles  from  the  mouth  of  the  river.  A  larger  amount  is 
deposited  at  the  mouth,  where  the  current  is  neutralized  by 
the  gulf  water.  This  deposit  forms  what  is  called  the  bar 
of  the  Mississippi,  which  so  much  obstructs  navigation.  It 
increases  at  such  a  rate  that  it  advances  336  feet  every  year, 
The  whole  amount  of  sediment  carried  down  by  the  Missis- 
sippi, if  dried,  would  make  every  year  a  pile  a  mile  square 
and  268  feet  high.  Much  of  the  Mississippi  sediment  is 
spread  over  the  region  of  the  overflow,  and  is  many  feet 
deep.  This  deposit  forms  the  delta,  of  the  Mississippi. 

All  streams  emptying  into  the  sea  carry  more  or  less 
sediment.  So  the  sea  bottom  is  becoming  covered  with  lay- 
ers of  mud ;  and  with  the  mud  must  be  mingled  the  remains 
of  all  the  animals  which  perish  in  the  sea. 

EXERCISES. 

Mention  some  marsh  with  which  you  are  acquainted.  Is  it 
quite  level  ?  What  once  existed  in  its  place  ?  Why  is  the  lake- 
let not  there  still  ?  What  is  the  upper  stratum  of  the  marsh 
composed  of  ?  If  you  should  find  much  earth  or  sand  mixed  with 
the  peat,  how  would  you  explain  that  ?  If  you  should  find  white 
shells  in  the  peat,  how  could  that  be  explained  ?  Is  the  peat 
chiefly  organic  or  inorganic?  Is  peat  of  any  use  to  the 
farmer  ?  What  is  the  use  of  marl  ?  What  is  the  composi- 
tion of  marl  ?  Is  the  bar  of  a  river  composed  chiefly  of 


IN   THE   GORGE.  87 

fine  or  of  coarse  matter?  How  does  the  sediment  far  from  a 
river's  mouth  compare  with  that  near  the  mouth  ?  Can  any 
sediment  get  into  the  sea  except  that  brought  down  by  rivers  ? 
Why  is  the  border  of  the  lake  or  the  sea  lined  with  pebbles  and 
cobble  stones  ?  When  the  waves  wear  away  a  gravel  bank,  what 
becomes  of  the  sand  and  clay  ?  If  you  could  dig  through  the 
layers  of  sediment  in  the  bottom  of  the  pond,  or  in  the  bottom 
of  the  Gulf  of  Mexico,  would  you  find  all  exactly  alike  ?  Why 
are  some  coarser  than  others  ?  Why  are  they  of  different  colors? 
Has  the  Hudson  River  any  delta?  What  might  prevent  a  river 
from  having  a  delta?  Mention  some  rivers  having  extensive 
deltas.  Why  are  some  rivers  clear  and  others  turbid  ? 


EXCURSION  XVIL—  In  the  Gorge. 
Decay  and  Erosion  of  Rocks. 

You  saw  how  large  an  amount  of  sediment  accumulates 
in  ponds  and  lakelets  ;  how  much  is  carried  down  by  rivers, 
and  how  the  sea  is  actually  filling  up  through  the  processes 
of  sedimentation.  Now,  all  this  sediment  comes  from  some- 
where. Let  us  see  if  we  can  find  the  sources  of  it. 

The  muddy  stream  by  the  roadside  —  well,  you  are  ready 
to  say  at  once  that  the  mud  comes  from  the  street.  Yes, 
that  accumulation  of  stones  and  sand  which  we  examined  at 
the  foot  of,  the  slope  is  nothing  but  stuff  washed  down  from 
the  roads.  Just  above  is  a  deep,  rugged  gully  washed  out 
by  the  rain.  Look  at  it.  Where  has  the  stuff  gone  which 
came  out  of  that  hole  ?  Is  it  all  at  the  foot  of  the  hill  ?  Is 
there  no  more  deposited  there  than  was  washed  out  here  ? 
The  wearing  away  of  the  ground  we  call  erosion. 

Now  we  have  reached  the  ravine.     This  is  on  a  hillside. 


88 


GEOLOGICAL   EXCURSIONS. 


The  hill  may  not  be  very  steep,  but  it  causes  water  to  flow 
down.  There  is  a  little  brook  here  which  is  always  running. 
Look  in  the  bed  of  the  brook  ;  why  is  it  so  stony  ?  Has 
there  been  no  soil  there,  nor  sand  ?  Here  in  the  bank  are 
sand  and  loam,  and  the  only  reason  why  such  fine  materials 
are  not  in  the  bed  of  the  stream  is  that  the  water  has  washed 
them  away.  The  sand  and  loam  have  gone  down  to  the 
flat,  and  very  likely  we  might  find  them  there  spread  out  just 
like  the  stuff  brought  down  by  the  roadside  torrent,  which 
only  worked  one  afternoon.  But  sometimes  this  stream  is 

vastly  larger  than  at  present; 
then  it  moves  the  larger  stones ; 
and  as  these  are  taken  away, 
others  come  from  higher  up. 
And  when  the  water  is  high  it 
washes  these  banks,  and  re- 
moves sand  and  stones,  and  in 
this  way  makes  the  ravine  wider. 
Think  of  that ;  the  stream  wid- 
ens this  ravine  every  year.  We 
can  think  of  a  time  when  the 
ravine  was  much  narrower,  and 
also  shallower.  We  can  think 
back  to  the  time  when  the  ra- 
vine first  began  to  be  formed. 

Ita.  SI-VIEW  IN  THK  GOEOE  At  V™*™t  it  is  broad  and  deep; 
AT  W  ATKINS'  GLEN,  N.  Y.  but  it  appears  that  it  has  all 
(-EAINBOW  FALLS  »),  Inus-  hag  been  d  out  fe  ^  wat(Jr 

TEATING    EROSION    BY     WATER. 

(PHOTOGRAPH.)  which    has    flowed    down    the 


THE   GORGE. 


89 


hillside.  If  this  hill  had  not  so  many  stones  and  rocks 
in  it,  the  rapine  would  have  become  much  deeper  than  it  is. 
In  Alabama,  where  stones  are  fewer,  or  at  least  smaller,  you 
can  see  deeper  ravines  excavated  during  one  man's  lifetime. 
Unless,  however,  the  rocks  are  of  the  crystalline  and 
quartzose  sorts  commonly  found  in  boulders,  it  seems  to 
make  little  difference  whether  the  sides  of  the  ravine  are 
rocky  or  mere  incoherent  drift.  We  could  visit  hundreds  of 
localities  where  some  little  stream  has  cut  deep  through  solid 
strata.  At  Watkins'  Glen,  in  southern  New  York,  is  a  very 
wild  and  interesting  spot.  Some  of  you  will  visit  that  spot 
Fig.  21  is  a  picture  which  all  can  examine.  Is  it  not  strange 
that  mere  water  could  wear  away  the  solid  rocks  on  so  vast 


FIG.  22.— THE  "DALLES"  OF  THE  WISCONSIN, 
SHOWING  RIVER  EROSION.     (PHOTOGRAPH.) 


90 


GEOLOGICAL   EXCURSIONS. 


a  scale  ?  It  is  a  fact,  nevertheless,  and  all  the  material  has 
gone  somewhere.  Let  us  look  on  the  map  and  ascertain 
where.  Here  is  Watkins  in  Schuyler  county,  at  the  head 
of  Seneca  Lake,  and  here  is  the  tiny  stream  which  has  worn 
the  gorge.  The  stuff  has  certainly  gone  into  Seneca  Lake, 
and  lies  spread  over  the  bottom. 

In  Figure  22,  is  a  similar  example  from  quite  another 
portion  of  the  country.  The  Wisconsin  River  has  cut  its 
gorge  through  the  ancient  strata,  forming  a  scene  of  beauty 
as  well  as  of  geological  interest.  A  grand  example  of  the 

work  of  a  mightier  stream  may 
be  seen  along  the  banks  of  the 
Upper  Mississippi  Biver  in 
Wisconsin  and  Minnesota. 
Here  a  wide  valley  has  been 
excavated  through  vast  forma- 
tions of  sandstone  and  lime- 
stone, and  the  walls  of  rock  rise 
on  each  side  one  or  two  hun- 
dred feet:  Between  them  flows 
the  broad  Mississippi.  (See 
Figure  23.  Also  Figure  51.)  In 
the  Far  West  is  a  river  known 
as  the  Colorado  which  has 
worn  a  gorge  in  some  places 
more  than  a  mile  in  depth. 

F».  23.-CL,™  o.   THE  UPPEK          But  the  rocks  everywhere 

MISSISSIPPI  NEAR  TREMPEALEAU,  ^e   wearing    out.      The    very 
Wis.,  ILLUSTRATING  RIVER  ERO-  , 

SIGN.    (CHAMBERLIN.)  rain  and  dew  tend  to  dissolve 


IN   THE   GORGE. 


91 


the  cement  which  holds  their  parts  together ;  and  freezing 
and  thawing  are  powerful  agents  in  disintegrating  them. 
You  will  recall  what  was  said  of  kaolin  as  simply  the  result 
of  decomposition  of  feldspar.  In  the  southern  states,  and  in 
all  warm  countries,  you  may  sometimes  trace  the  encroach- 
ment of  decay  from  the  exposed  surface  of  a  bed  rock  down- 
ward ten  or  twenty  feet.  All  over  the  land  the  rocks  are 
decaying,  and  the  rains  wash  the  powder  and  the  grains  into 
the  streams  ;  and  this  is  the  source  of  much  of  the  sediment 
which  floats  in  the  rivers  and  spreads  over  the  sea  bottom. 
It  is  calculated  that  the  surface  of 
the  land  is  lowered  a  foot  in  six 
thousand  years.  Of  course  some 
rocks  decay  faster  than  others. 
Sometimes  rocks  are  undermined 
by  the  more  rapid  decay  of  the 
rocks  beneath  them.  Here  is  an 
interesting  case  in  Wisconsin  in 
the  bluff  of  a  creek.  In  many 
cases  cubic  miles  of  rock  have 
been  eroded  and  removed  from 
the  midst  of  the  land.  All  the  central  part  of  Tennessee 
is  a  vast  basin  sunk  through  the  solid  limestone.  All 
around  the  border  the  remaining  limestone  rises  in  massive 
walls  a  hundred  feet  high  and  more.  In  east  Tennessee  is 
another  valley  formed  by  extensive  erosion.  These  are  shown 
in  the  cut,  Figure  25.  See,  also,  how  the  nearly  vertical  strata 
of  the  Unaka  range  have  been  worn  down  to  mere  stumps. 
Where  have  gone  the  continuations  of  those  upturned  strata  ? 


FIG.  24. 

MAGNESIAN  LIMESTONE  UNDER- 
MINED BY  THE  DISINTEGRA- 
TION OF  A  SANDSTONE  BE- 
NEATH. (CHAMBERLIN.) 


92 


GEOLOGICAL   EXCURSIONS. 


See  the  wonderful  proof  of  vast 
erosions  along  the  Appalachians. 
(Figure  26. )  Here  the  actual  sur- 
face is  shown  along  ABC.  Can 
you  believe  that  the  slight  ele- 
vation at  A  represents  truly  one 
of  the  ranges  of  the  Allegheny 
Mountains  ?  And  that  B  repre- 
sents the  range  known  as  Bald 
Eagle  Mountain  ?  How  the 
vast  series  of  strata  has  been 
folded  here.  Notice  the  moun- 
tain mass  represented  by  E, 
which  once  rose  thirty-five  thou- 
sand feet  above  the  present  sur- 
face, and  all  has  been  carried 
away  by  erosion.  This  section 
is  in  Centre  county,  and  shows 
but  a  fraction  of  a  full  section 
across  the  Appalachian  chain. 
But  all  the  mountain  elevations 
have  been  similarly  worn  down. 
In  other  cases  singular  col- 
umns of  the  eroded  rock  have 
escaped  erosion.  They  have 
been  protected  by  a  fragment  of 
harder  rock,  which  rests  on  them 
like  a  cap.  Lr'Monument  Park," 
Colorado,  are  many  remarkable 
examples.  (See  Figure  27.) 


IN   THE   GORGE. 
**> 


93 


FIG.  26. — ILLUSTRATING  ENORMOUS  EROSION  IN  THE  APPALACHIAN  REGION. 
A,  Allegheny  Mountain  at  Snow  Shoe ;  B,  Bald  Eagle  Mountain ;  A,  B, 
C,  present  surface  —  all  above  swept  away ;  D,  probably  a  subterranean 
mountain  of  Eozoic  rocks;  II  to  III,  Cambrian;  IV  to  VI,  Silurian;  VII 
to  IX,  Devonian;  X  to  XII,  Lower  Carboniferous;  XIII,  Coal  Measures 
(after  Lesley).  Compare  for  explanations,  Excursion  XVIII. 

So  we  learn  there  has  been  a  vast  destruction  of  the  rocks 
during  the  course  of  many  ages.  They  have  been  gradually 
reduced  to  gravel  and  mud,  and  carried  off  by  the  streams, 
to  be  laid  down  on  the  plains  or  spread  as  sediment  over  the 
bottom  of  the  sea.  Other  interesting  cases  of  erosion  are 
shown  in  Figures  52,  53,  60,  61  and  73. 

EXERCISES. 

Can  a  quartzite  be  worn  out  by  any  means?  If  quartz  peb- 
bles are  fragments  of  rocks,  why  are  they  not  sharp  angled? 
Which  wears  fastest,  a  quartzite  or  a  limestone?  If  water  flows 
through  a  fissure  in  a  limestone,  by  what  two  means  will  the 
fissure  be  enlarged  ?  If  the  fissure  is  underground,  what  will  it 
become  ?  Are  many  caverns  produced  in  this  way?  Which  make 
the  steepest  banks  to  a  stream,  hard  rocks  or  soft  ones  ?  Why 
are  not  the  walls  of  all  gorges  nearly  perpendicular?  Does 
weathering  affect  the  angles  of  cliffs  and  rock  fragments  ?  What 
sort  of  climate  would  weather  the  rocks  most  rapidly?  Would 
vertical  cliffs  be  most  likely  to  stand  in  a  dry  climate,  or  a  change- 
able one  ?  In  a  climate  with  freezing  and  thawing,  or  one  with 


94  GEOLOGICAL  EXCURSIONS. 

no  freezing?  What  is  the  difference  between  erosion  and 
weathering  ?  Which  kind  of  work  is  done  by  running  streams  ? 
Which  is  done  by  waves?  Which  is  done  by  frost?  Is  there 
any  important  difference  between  the  wearing  done  by  rains  and 
that  done  by  streams?  Is  it  running  water  which  has  made  the 
valleys  in  a  country  completely  drift  covered  ?  Why  have  the 


FIG.  27. — COLUMNS  IN  MONUMENT  PARK,  COLORADO.    (HAYDEN.) 

valleys  such  sloping  banks?  Has  floating  ice  any  influence  on 
the  work  of  running  waters?  Explain  a  possible  origin  of  a 
natural  bridge.  Explain  a  possible  origin  of  the  Mammoth  Cave 
of  Kentucky.  What  effect  has  erosion  on  the  farmer's  soils? 
Does  any  of  his  soil  go  where  no  one  can  find  it  again?  What 
effect  has  erosion  on  the  height  of  the  hills? 


AT   THE    ROCKY    LEDGE.  95 

EXCURSION  XVIIL—  At  the  Rocky  Ledge. 
Strata  and  Systems  of  Strata. 

You  have  seen  the  brooks  and  rivers  at  work  wearing 
down  the  land.  You  have  seen  the  waves  corroding 
the  beach.  You.  have  thought  on  the  slow  disintegration 
of  all  the  surface  rocks  by  rains  and  frosts,  and  have  seen 
the  waters  carrying  away  the  sediments  to  the  sea.  In 
thought  you  have  followed  those  sediments  in  their  distri- 
bution over  the  ocean's  bottom.  You  have  seen  them 
lying  and  accumulating  there,  while  dead  shells  and  bits  of 
coral  and  bones  of  fishes  have  been  mingled  with  the  grow- 
ing deposit.  What  appearance  must  these  sediments  present 
in  case  a  few  acres  of  sea  bottom  could  be  taken  out  bodily 
and  inspected  ?  The  sediments  would  consist  of  layers 
parallel  with  each  other,  one  above  another.  These  layers 
would  be  distinguished  by  different  colors  and  by  different 
degrees  of  fineness.  Imbedded  in  the  substance  of  the 
layers  would  bo  the  relics  of  the  animals  which  have  lived 
in  the  sea.  Is  this  a  correct  statement  of  what  you  would 
see  ?  Think  about  it.  The  depth  of  the  accumulated  sedi- 
ments would  correspond  to  the  time  spent  in  their  accumu- 
lation. You  might  look  at  them  and  reflect:  "These  layers 
of  mud  and  sand  were  once  far  inland.  They  were  once 
part  of  the  soil  of  cornfields  and  gardens.  Crops  grew  on 
them.  The  gully  in  the  road  was  made  by  the  removal  of 
them.  They  came  down  the  rivers.  Some  started  on  the 
slopes  of  distant  mountains.  The  Missouri  brought  some 
from  the  gorges  and  summits  of  the  Rocky  Mountains. 


96  GEOLOGICAL   EXCURSIONS. 

Some  came  out  of  the  deep,  dim  canyons  of  the  Colorado. 
Some  came  from  the  storm-torn  bluffs  at  Long  Branch  or 
Coney  Island  or  Gay  Head.  Some  was  yielded  by  the  slowly 
dissolving  promontories  of  Nahant  and  Marblehead." 

That  is  what  you  might  think.  Now  suppose  the  layers 
of  sediments  pressed  by  thousands  of  tons  of  weight.  They 
would  be  pressed  into  a  solid  state, —  like  the  paper  pulp 
which  is  manufactured  into  car-wheels.  They  would  be  a 
rock.  The  rock  would  be  composed  of  strata.  The  thin 
layers  would  be  called  laminae.  The  shells  and  corals 
pressed  in  the  rock  would  be  fossils.  This  is  almost 
exactly  what  we  have  in  the  majority  of  the  rocks  under- 
lying the  country.  All  our  limestones,  sandstones  and 
shales  were  once  just  such  sea-sediments.  The  limestones, 
however,  contain  a  very  large  proportion  of  matters  con- 
tributed by  the  decay  of  shell-bearing  animals. 

In  most  of  New  England,  however,  and  along  the  north- 
ern border  of  our  country,  the  ledges  of  rocks  which  we 
find  are  hard  and  crystalline.  From  these  have  come  most 
of  the  boulders  which  are  scattered  over  the  surface  of  all 
the  northern  states.  In  places  where  these  crystalline  rocks 
come  in  contact  with  the  uncrystalline,  we  find  the  uncrys- 
talline  overlying  the  others.  (See  Figure  28.)  But  there 
are  almost  always  some  traces  of  stratification  even  in  the 


b  a  be 

FIG.  28. — CRYSTALLINE  AND  UNCRYSTALLINE  ROCKS,    a,  Granite;  b,  Gneiss; 

c,  Sandstone. 


AT   THE   KOCKY    LEDGE.  97 

crystalline  rocks.  You  remember  the  gneisses  and  schists. 
Well,  this  is  the  way  they  lie  over  the  granite  and  beneath 
the  sandstones.  They  have  been  rendered  less  distinctly 
stratified  by  some  action  called  metamorphism.  What  are 
the  particulars  of  that  action  cannot  now  be  explained;  but 
you  may  understand  that  great  pressure,  great  heat  and 
chemical  operations  have  had  much  to  do  with  metamor- 
phism. If,  then,  even  the  hard  crystalline  rocks  were  also 
once  sea  sediments,  they  must  have  been  laid  down  before 
the  sediments  which  formed  the  uncrystalline  rocks.  That 
is,  older  rocks  are  below,  and  newer  rocks  are  above. 

In  the  crystalline  rocks  it  is  a  very  extraordinary  thing 
to  find  any  fossils.  In  the  uncrystalline  rocks  it  is  a  com- 
mon thing.  So  this  is  another  particular  in  which  they 
differ. 

But  now  let  me  tell  you  something  very  important  about 
the  uncrystalline  rocks.  We  do  not  find  the  same  kinds  of 
fossils  in  all  of  them.  Those  at  the  bottom  contain  many 
relics  of  very  strange  creatures,  and  they  are  all  marine. 
There  are  none  which  lived  on  the  land.  There  are 
none  which  had  back-bones.  That  is,  they  were  all  in- 
vertebrate. In  strata  which  overlie  these  we  find  the 
teeth  and  bones  of  fishes;  but  still  the  fossils  are  all  marine. 
Still  higher,  we  find  strata  with  the  remains  of  creatures 
which  dwelt  on  the  land;  but  they  were  sluggish,  salaman- 
der-like creatures.  When  we  come  to  rocks  overlying 
these,  we  find  in  them  the  bones  of  an  astonishing  number 
of  reptiles.  Still  higher  we  find  bones  of  quadrupeds.  This 
is  all  very  curious;  but  it  shows  that  the  rocks  may  be 


98  GEOLOGICAL  EXCURSIONS. 

classified  according  to  the  fossil  remains  which  they  con- 
tain. Let  us  repeat  the  succession:  1.  Rocks  almost  with- 
out fossils.  These  are  at  the  bottom.  2.  Rocks  containing 
only  marine  invertebrates.  3.  Rocks  containing  marine  ver- 
tebrates. 4.  Rocks  containing  the  lowest  terrestrial  verte- 
brates. 5.  Rocks  containing  the  remains  of  reptiles  and 
birds.  6.  Rocks  containing  the  remains  of  mammals. 

Now,  the  reason  why  the  rocks  containing  marine  inver- 
tebrates do  not  contain  also  marine  vertebrates,  or  land 
animals  of  any  kind,  is  because  these  other  animals  were 
not  in  existence  when  the  lower  rocks  were  accumulating  as 
sediments.  And  so  we  learn  that  the  different  ranks  of 
animals  were  called  into  existence  at  different  times.  There 
has  been  a  succession  and  a  progress  in  the  history  of  life 
on  the  earth. 

These  are  some  of  the  most  important  facts  in  geology. 
Each  of  these  series  of  rocks  is  called  a  system  /  and  each 
system  has  received  a  name.  It  is  extremely  important 
to  commit  these  names  to  memory.  Here  in  this  diagram 
(Fig.  29)  they  are  all  arranged  in  order,  with  the  char- 
acteristic fossils  indicated.  All  this  must  be  well  studied. 

Take  notice.  You  are  learning  now  only  the  order  of 
superposition  of  strata,  and  the  systems  in  which  they  are 
classified.  Do  not  think  all  these  rocks  can  be  found  piled 
up  in  every  place.  You  shall  learn  next  time  we  meet  how 
the  various  strata  are  distributed  over  the  country. 


GREAT  SYSTEMS, 

OR 
ERAS. 


C.ENOZOIC. 


MESOZOIC. 


SYSTEMS, 

OR 
AGES. 


QUATERNAKY. 

TERTIARY. 

CRETACEOUS. 

JURASSIC. 
TRIASSIC. 

UPPER  CAR- 
BONIFEROUS. 

LOWER  CAR- 
BONIFEROUS. 


PALAEOZOIC.      DEVONIAN. 


Eozoic. 


UPPER  SILU- 
RIAN 

(OR  SILURIAN). 

LOWER   SILU- 
RIAN 
(OR  CAMBRIAN). 


HURONIAN. 


LAURENTIAN. 


Star  Peak  Group. 
Koipato  Group. 
Permian. 


HIGHEST 
FOSSILS. 


Carbonif.  Limestone. 

Catskill  Group. 
Chemung  Group. 
Hamilton  Group. 
Comijerous  Group. 
Oriskany  Sandstone. 
Helderberg  Group. 
Salina  Group. 
Niagara  Group. 

Trenton  Group. 

Canadian  Group. 
Primordial  Group. 


W     M 


FIG.  29. — THE  GEOLOGICAL  COLUMN. 


100  GEOLOGICAL   EXCURSIONS. 

EXERCISES. 

What  two  systems  are  included  in  the  Eozoic  Great  System  ? 
What  are  included  in  the  Palaeozoic  Great  System  ?  What  in  the 
Mesozoic  ?  What  in  the  Caenozoic  ?  Which  are  the  oldest  strata, 
the  Devonian  or  the  Cretaceous  ?  Do  we  find  any  fossil  men  in 
the  Silurian  ?  Were  there  any  snakes  in  the  Eozoic  ?  Are  there 
any  snakes'  remains  in  the  Caenozoic  ?  Are  whales  marine  verte- 
brates ?  Are  there  any  whales'  remains  in  the  Devonian  ?  What 
do  you  understand  by  the  Devonian  Age  ?  What  is  meant  by 
the  Cretaceous  Age  ?  Which  was  the  longest,  an  Era  or  an 
Age  ?  What  are  the  Ages  of  the  Palaeozoic  Era  ?  Did  the 
continent  of  America  exist  during  the  Palaeozoic  Era?  Which 
are  the  hardest,  Palaeozoic  or  Caenozoic  rocks  ?  Which  were 
hardest  when  first  laid  down  as  sea-sediments  ?  What  do  we 
call  that  process  by  which  the  Eozoic  rocks  became  crystalline  ? 
Mention  several  kinds  of  Eozoic  rocks.  Are  most  of  our  boul- 
ders derived  from  Eozoic  or  from  newer  rocks  ?  Why  do  the 
Eozoic  rocks  appear  less  distinctly  stratified  than  the  Palaeozoic  ? 
Suppose  we  find  a  shale  in  contact  with  mica  schist,  which  do 
you  think  the  oldest  rock  ?  Which  would  lie  above  the  other  ? 
Could  you  expect  to  find  a  chalk  under  a  granite  ?  Why  not  ? 
Would  it  be  possible  for  mud  in  the  bar  of  the  Mississippi  ever 
to  become  solid  rock  ?  What  kind  of  a  rock  do  you  imagine  it 
would  make  ?  Could  it  possibly  become  chalk  ?  Could  it  possi- 
bly become  granite  ?  Could  that  mud  be  changed  to  limestone 
by  any  means  ?  Was  the  Mississippi  mud  ever  solid  rock  ?  Were 
the  solid  rocks  ever  mud?  What  is  the  use  of  making  rocks  and 
then  wearing  them  into  mud  to  make  rocks  of  again  ? 


TO   THE    DIAGRAMS. 


V101 


EXCURSION  XIX.—  To  the  Diagrams.  J 
How  the  Strata  Enwrap  the  Earth. 


FIG.  30. — THE  SYSTEMS  OF  STRATA  NOT  LIKE  THIS. 

If  yon  cut  an  onion  through  the  middle  in  such  a  direc- 
tion that  the  top  is  on  one  half  and  the  root  on  the  other, 
the  layers  of  the  onion  will  be  seen  surrounding  each  other 
somewhat  like  the  bands  A,  B,  C,  D,  in  this  figure.  But 
this  does  not  represent  the  way  the  different  systems  of 
strata  enwrap  the  earth.  You  have  learned  that  all  the 
rocks  have  been  sea-sediments  at  some  time.  You  know 
from  this  that  wherever  the  rocks  are,  there  has  been  the 
sea.  As  there  is  some  kind  of  rocks  —  that  is,  some  system 
of  rocks  —  at  every  place,  we  may  be  certain  that  the  sea 
has  covered  every  place  at  some  time.  But  it  is  not  true 


102 


GEOLOGICAL    EXCURSIONS. 


that  all  the  Systems  of  rocks  are  present  under  every  place. 
If  they  were  we  should  have  everywhere  the  Csenozoic  rocks 
at  the  surface,  and  under  these  would  be  the  Mesozoic,  and 
then  would  follow  downward  the  Palaeozoic  and  the  Eozoic. 
The  fact  is  that  any  system  of  rocks  may  be  at  the  surface. 
Sometimes  even  the  Eozoic  rocks  are  at  the  surface;  and,  in 
fact,  we  sometimes  find  them  thousands  of  feet  above  the 


FIG.  31. — THE  SYSTEMS  OF  STRATA  MORE  LIKE  THIS. 

level  of  the  sea.     This  state  of  things  it  is  very  important 
to  understand. 

It  appears  that  the  earth  has,  at  various  times  in  the 
past,  been  a  little  distorted  in  shape,  as  you  may  see  in 


TO   THE   DIAGRAMS.  103 

Figure  31;  though  you  must  not  think  the  earth  has  been 
squeezed  into  such  a  shape.  It  has  not  been  distorted  one- 
hundredth  so  much  as  this.  Such  a  figure  is  given  to  make 
it  easier  for  you  to  see  the  effects  of  distortion.  In  this 
figure  we  may  suppose  the  bands  A,  B,  C,  d  to  represent 
the  different  systems  of  rocks  as  they  would  appear  if  the 
earth  were  cut  through,  through  the  middle.  All  these 
bands  are  near  the  surface.  We  cannot  show  anything  in 
the  interior  of  the  earth,  because  we  do  not  know  what  is 
there.  We  can  guess  something  about  it;  but  we  must 
confine  ourselves  now  to  that  part  of  the  earth  which  is  very 
near  the  surface.  That  part  which  we  know  to  be  composed 
of  solid,  rocky  material  is  called  the  earth's  Crust.  In  this 
we  have  the  various  systems  marked  A,  B,  C,  d,  the  names 
of  which  you  learned  in  the  last  lesson.  The  figure  shows  a 
section  through  the  crust,  and  shows  how  one  system  of 
rocks  overlies  another.  Where  any  stratum  goes  down 
under  another,  we  say  it  dips  under  it.  When  it  comes  out 
from  under  another,  we  say  it  outcrops. 

You  will  notice  that  the  only  system  which  completely 
surrounds  the  earth  is  the  Eozoic,  A.  In  some  places  the 
Eozoic  comes  quite  to  the  surface;  in  others,  as  at  #,  #,  #,  #, 
it  is  overlaid  by  all  the  other  systems.  In  other  places,  as 
at  5,  £,  5,  it  is  overlaid  only  by  the  Palaeozoic.  In  still 
other  places,  as  at  0,  c,  0,  <?,  it  is  overlaid  by  both  Palaeozoic, 
B,  and  Mesozoic,  C.  There  are  only  a  few  places,  like  d,  d', 
d",  where  any  Csenozoic  can  be  seen  —  except  Drift  or  other 
Post-Tertiary,  which  covers  nearly  all  the  earth's  surface, 
and  is  not  represented  in  this  diagram.  In  some  places, 


104  GEOLOGICAL   EXCURSIONS. 

like  ft',  the  Tertiary  (Caenozoic)  rests  directly  upon  the  Pa- 
laeozoic, or  even  the  Eozoic. 

If  you  look  closely  at  this  diagram  you  notice  an  appear- 
ance as  if  the  Palaeozoic  and  Mesozoic  strata  had  at  some 
former  time  extended  much  further  than  at  present.  For 
instance,  the  dotted  line  c'  c'  shows  what  may  have  been  at 
some  time  the  upper  surface  of  the  Mesozoic.  If  so,  then 
the  dotted  line  below  this  shows  what  may  have  been  at 
the  same  time  the  upper  surface  of  the  Palaeozoic.  In  fact, 
on  all  sides  the  arrangement  of  the  strata  looks  as  if  they 
had  been  once  wrinkled  up,  and  then  the  higher  places 
removed.  That  is  something  like  the  truth.  But  we  must 
not  suppose  the  Palaeozoic  and  Mesozoic  ever  extended 
quite  over  all  the  Eozoic  which  is  now  at  the  surface.  We 
cannot  say  precisely  how  far  they  ever  covered  the  Eozoic. 
We  are  certain,  however,  that  they  have  been  eroded  to  a 
great  extent.  And  we  can  understand  that  the  sediment 
produced  by  such  erosions  went  partly  into  the  sea,  and  was 
made  over  in  the  patches  of  Tertiary  which  we  see  at  <#,  d, 
d,  d". 

If  the  dotted  circle  s  s  s  represents  the  level  of  the 
ocean,  you  see  that  some  parts  of  the  crust  rise  above  it  and 
form  the  continents  ;  and  those  parts  which  rise  highest  are 
mountains.  You  see,  also,  that  all  the  systems  of  strata  lie 
under  the  sea. 

Now  fix  your  attention  on  the  d  near  the  lower  side  of 
the  diagram,  a  little  to  the  left  of  the  middle.  The  rocks 
there  are  Caenozoic;  and  you  see  a  section  or  cut  right 
through  them  and  the  rocks  under  them.  This  section 


TO   THE    DIAGRAMS. 


105 


FIG.  32. — MAP  OF  THE  REGION 
AROUND  b  d  c,  FIG.  31. 


shows  what  is  the  surface  extent  of  the  Caenozoic  area  there 
in  one  direction.  Here  it  is,  the 
distance  from  m  to  n  in  this  lit- 
tle cut  (Figure  32).  We  do  not 
know  how  broad  this  Caenozoic 
area  is  in  the  other  direction ; 
but  let  us  suppose  it  a  little  ob- 
long; then  its  other  diameter  will 
be  o  p,  and  m  p  n  o  will  be  a 
map  of  the  Csenozoic  area  of 
which  a  section  is  shown  in  Fig- 
ure 31  at  d,  near  the  lower  side 
of  the  figure. 

But  then,  on  one  side  of  this 
Csenozoic  section  is  a  section  of 
Mesozoic  strata.  Let  us  take  the  length  of  this  Mesozoic 
section  and  lay  it  off  from  m  to  r  on  the  side  of  the  map, 
Figure  32.  As  the  Mesozoic  on  the  other  side  is  covered  by 
the  sea,  we  may  represent  the  sea  as  bordering  the  Cseno- 
zoic, and  may  lay  down  as  much  of  it  as  we  please, —  say 
from  n  to  £,  on  the  other  side  of  the  map;  and  may  assume 
that  the  sea-shore  leaves  the  Caenozoic  area  at  «,  s.  Then 
the  distance  from  r  across  to  n  is  the  whole  diameter  of  the 
Mesozoic  area,  to  the  sea, —  including  the  portion  covered 
by  the  Caenozoic.  The  breadth  in  the  other  direction  is  not 
known;  but  we  may  assume  it  as  extending  from  t  to  u. 
The  whole  size  of  the  Mesozoic  area  not  covered  by  the  sea 
will  therefore  be  shown  by  v  t  r  u  w.  Lastly,  the  Palaeo- 
zoic, when  laid  down  on  a  map,  will  give  a  belt  surrounding 


106 


GEOLOGICAL   EXCUKSIONS. 


the  Mesozoic,  as  shown  in  x  y  z.  So  this  is  a  geological 
map  showing  three  systems  of  strata;  and  Figure  33  shows 
the  appearance  of  a  section  across  it. 

Now,  once  more.     Fix  your  atten- 
tion on  the  point  G  in  Figure  31.     If 
^^L\-^/' -y/vj^^      we   proceed   to  make   a  map  of  the 
FIG.  33.— SECTION  ALONG    region  around  this  point,  it  will  look 
THE  LINE  y  q,  FIGURE    something  like  Figure  34.      Here  you 
see  the  Eozoic  in  the  middle  and  the 
newest  strata  around  the  bor- 
der.     Here,   also,   the   ocean 
bounds  the  area  on  one  side. 
Notice  particularly  the  differ- 
ence  between   this   map   and 
the  other.     There  the  strata 
dipped  from  all  sides  toward 
the  centre;  here  they  dip  from 
the  centre  toward  all  the  sides. 
This  is  shown  in  the  section, 
Figure   35,  where   the  Meso- 
zoic c  dips  under   the  ocean 
on  one  side ;  the  Palaeozoic  b 
dips  under  the  Csenozoic,  and 


FIG. 


34.  —  MAP   OF   THE   REGION 
AROUND  G,  FIG.  31. 


FIG.  35.— SECTION  ALONG  THE  LINE 
d  s,  FIG.  34. 


extends  on  one  side  under 
the  ocean ;  and  the  Eozoic  G- 
dips  in  both  directions  under 
the  Palaeozoic. 

Now,  before  we  pass  on  to 
the  study  of  the  geological 


LAVA, 


TRACHYTE 


BASALT 


GRANITE 


GRANITE 
VEIN 


FIG.  36. — IDEAL  SECTION  OF  THE  EARTH'S  CRUST. 


108  GEOLOGICAL   EXCURSIONS. 

map,  look  at  this  more  extensive  section  through  the  rocks 
of  the  earth's  crust.  This  is  not  intended  to  show  what 
would  be  seen  in  any  particular  region,  but  would  be  seen 
in  a  good  many  different  regions.  The  various  geological 
phenomena  which  would  be  seen  in  many  different  regions 
are  here  all  brought  together.  So  this  is  not  a  Teal  but  an 
ideal  section.  Still  everything  shown  is  real  somewhere. 
This  section  will  bear  a  great  deal  of  study.  You  cannot 
learn  all  about  it  now.  I  intend  that  you  shall  turn  back  to 
it  a  great  many  times.  But  you  may  now  ask  as  many 
questions  about  it  as  you  please. 

EXERCISES. 

In  Figure  32,  if  we  travel  from  the  centre  to  the  circumfer- 
ence, do  we  pass  from  newer  to  older  rocks,  or  from  older  to 
newer  ?  If  we  stand  near  the  circumference,  which  way  do  the 
strata  dip  ?  Do  they  dip  toward  and  under  newer  strata,  or  away 
from  them  ?  If  we  bore  a  deep  hole  at  the  centre  of  Figure  32, 
what  systems  of  rocks  will  we  pass  through  ?  If  we  stand  near 
the  circumference  of  Figure  34,  which  way  do  the  rocks  dip  ? 
Do  they  dip  toward  the  older  rocks,  or  away  from  them  ?  Must 
strata  always  dip  TOWAED  NEWER  rocks  and  AWAY  FKOM  OLDEK 
rocks  ?  Suppose  you  bore  a  deep  hole  near  the  margin  of  Figure 
34,  what  systems  of  strata  would  be  passed  through  ?  Suppose 
you  bore  at  the  middle  of  Figure  34,  what  rocks  will  be  passed 
through  ?  Must  a  geological  area  necessarily  be  circular  ?  Sup- 
pose the  ocean  should  wear  away  two-thirds  from  the  area  mapped 
in  Figure  34,  could  you  then  make  a  geological  map  of  the 
region  ?  Try  it.  Point  out  places  where  the  Palaeozoic  outcrops 
in  Figure  31.  Show  where  the  Eozoic  outcrops.  What  system 
of  rocks  least  completely  enwraps  the  earth  ?  How  could  it  be 
that  Casnozoic  rocks  should  rest  on  Eozoic,  with  no  Palaeozoic  or 
Mesozoic  between  them  ?  Make  a  geological  map  of  the  region 


TO   THE   GEOLOGICAL   MAP.  109 

extending  from  G  toward  the  left,  through  c,  d  and  s,  to  b,  in 
Figure  31. 


EXCURSION"  XX.—  To  the  Geological  Map. 
How  to  Understand  a  Geological  Map. 

I  will  now  help  you  to  understand  a  geological  map  of 
the  United  States.,  Here,  in  Figure  37,  is  such  a  map  ex- 
tended as  far  west  as  the  Black  Hills.  This  is  a  real  map 
which  attempts  to  represent  things  as  they  are.  In  the  cor- 
ner of  the  map  is  a  "legend,"  which  indicates  what  sys- 
tems of  strata  are  mapped.  These  are  the  same  as  the 
"Systems"  in  the  "Geological  Column,"  Figure  29,  with 
three  exceptions  :  The  Laurentian  and  Huronian  are  here 
thrown  together  as  Eozoic ;  the  Triassic  and  Jurassic  are 
thrown  together  as  Jura-Trias,  and  the  Post  Tertiary  is  dis- 
regarded, since  this  is  understood  to  be  everywhere  present, 
covering  all  other  formations. 

First,  fix  your  attention  on  the  areas  marked  Eozoic.  One 
large  area  lies  north  of  the  Great  Lakes  and  the  St.  Law- 
rence Eiver;  another  lies  along  the  eastern  flanks  of  the 
Appalachian  chain  of  mountains  —  extending  from  Penn- 
sylvania through  Maryland,  Virginia,  North  and  South 
Carolina  and  Georgia  into  Alabama.  These  two  Eozoic 
masses  pass  under  all  the  intervening  strata  and  meet  to- 
gether. As  the  Eozoic  strata  are  the  oldest  known,  the 
strata  on  both  sides  of  an  Eozoic  area  must  be  newer  than 
Eozoic,  and  must  overlie  the  Eozoic.  As  the  dips  are 
always  away  from  the  older  rocks,  it  must  be  that  the  rocks 


TO   THE   GEOLOGICAL  MAP.  Ill 

along  the  eastern  side  of  the  Appalachian  Eozoic  dip  toward 
the  southeast,  and  those  along  the  western  side  toward  the 
northwest.  And  so  the  rocks  along  the  border  of  the 
Canadian  Eozoic  must  dip  directly  away  from  it.  That  is, 
along  the  valley  of  the  St.  Lawrence  River,  the  rocks  next 
the  Eozoic  must  dip  southeast ;  in  the  region  north  of  Lakes 
Ontario  and  Huron,  the  dip  must  be  south  ;  in  eastern  Wis- 
consin, the  dip  is  southeast,  and  in  western  Wisconsin,  it  is 
southwest. 

Southeast  from  the  Appalachian  Eozoic  we  have  very 
little  except  Tertiary  strata.  These  then  overlie  the  border 
of  the  Eozoic,  and  dip  southeastward,  extending  to  the 
Atlantic  Ocean.  Northwest  of  the  Appalachian  Eozoic  we 
find  strata  indicated  by  full  oblique  lines  in  one  direction 
and  broken  oblique  lines  in  the  other  direction.  These  are 
explained  in  the  u legend"  to  mean  that  the  rocks  are 
either  Cambrian  or  Silurian  (Lower  Silurian  or  Upper  Silu- 
rian, as  some  geologists  prefer  to  say),  but  we  have  not  yet 
ascertained  which.  These  must  dip  northwesterly,  away 
from  the  older  Eozoic,  and  toward  the  newer  Upper  Carbo- 
niferous. Passing  under  all  the  Carboniferous,  they  come 
to  the  surface  again  in  Tennessee,  Kentucky,  Ohio  and 
Indiana,  where  we  have  learned  them  well  enough  to  dis- 
tinguish both  Cambrian  and  Silurian  (or,  as  some  say,  Lower 
and  Upper  Silurian).  On  the  north,  Cambrian  and  Silurian 
corne  up  along  the  two  shores  of  Lake  Ontario.  From  this 
region  the  dip  is  southward  all  the  time  until  we  reach  cen- 
tral Pennsylvania.  In  southwestern  Ohio,  the  Cambrian 
which  comes  up  from  the  southeast  soon  dips  down  again 


112  GEOLOGICAL   EXCURSIONS. 

toward  the  northwest,  and  passing  under  Michigan  and  Lake 
Michigan,  comes  up  again  in  eastern  Wisconsin.  Now  try 
and  follow  the  Cambrian  and  Silurian  up  and  down  all  the 
way  from  the  Appalachian  Eozoic. 

You  must  not  be  content  to  simply  read  these  descrip- 
tions. You  must,  by  all  means,  follow  the  systems  of  strata 
on  the  map.  When  they  go  under,  your  thoughts  must  fol- 
low them.  When  they  appear  in  view  again,  your  thought 
must  see  them  coming  from  under  the  newer  strata.  You 
must  look  under  the  surface  of  the  map  and  see  the  solid, 
thick  crust  of  the  earth  with  its  various  strata  curved  and 
overlapping,  and  discontinuing  and  beginning  again,  disap- 
pearing arid  outcropping  just  as  I  describe  them.  If  you  do 
this,  and  perform  plenty  of  such  exercises  as  will  be  given 
you,  the  study  will  soon  be  easy  and  delightful.  If  you  do 
not,  you  will  never  have  a  good  knowledge  of  geology. 

Now  let  us  continue  the  explanation  of  the  map.  On  the 
southwestern  border  of  the  Wisconsin  Eozoic,  you  see  the 
Cambrian  overlying  it,  and  thence  dipping  southwesterly 
under  Silurian,  Devonian,  Lower  Carboniferous  and  Upper 
Carboniferous.  We  can  trace  it,  in  thought,  under  all  these 
systems  into  Missouri  and  Kansas.  We  might  reasonably 
expect  the  Eozoic  to  come  to  the  surface  again  in  the  region 
farther  southwest,  but  it  scarcely  succeeds  in  revealing  itself. 
You  will  notice  one  patch  in  the  Indian  Territory,  and  one 
in  southern  Texas ;  but  nearly  all  that  region  has  been  cov- 
ered by  Jura-Trias,  and  then  most  of  that  has  been  covered 
by  Cretaceous.  Even  upon  the  top  of  the  Cretaceous  are 
some  patches  of  Tertiary. 


TO  THE   GEOLOGICAL   MAP.  113 

In  New  England  you  will  notice  considerable  areas 
marked  Eozoic ;  but  in  some  cases  we  only  know  that  the 
rocks  are  crystalline  like  Eozoic,  while  they  may  be  in 
reality  only  later  rocks  hardened  and  crystallized  by  meta- 
morphism.  You  observe,  however,  a  patch  of  Upper  Car- 
boniferous in  Rhode  Island,  and  a  belt  of  Jura-Trias  running 
through  Connecticut  and  Massachusetts.  Farther  north  you 
will  notice  that  the  valley  of  the  Connecticut  is  underlaid  by 
Cambro-Silurian  rocks  —  that  is,  rocks  either  Cambrian  or 
Silurian. 

In  the  Adirondac  region  of  New  York  is  an  interesting 
Eozoic  area.  This  connects  with  the  Canadian  Eozoic  by  a 
narrow  neck  across  the  St.  Lawrence  River.  The  strata  all 
around  this  Adirondac  area  dip  away  from  it.  This  is  a  case 
somewhat  like  the  Eozoic  area  in  Wisconsin.  On  the  other 
hand,  the  centre  of  Michigan  is  an  area  of  Upper  Carbonif- 
erous, and  since  the  surrounding  strata  are  all  older,  they  all 
dip  toward  the  centre  of  Michigan. 

Now  let  us  vary  the  method  of  study.  Suppose  we  stand 
on  the  southern  side  of  Lake  Ontario,  the  map  shows  that 
the  dip  of  the  rocks  is  south  ;  for  at  that  point  we  have  Silu- 
rian, while  to  the  south  are  the  (newer)  Devonian  and  Lower 
and  Upper  Carboniferous ;  and,  according  to  the  rule,  the 
dip  is  toward  the  newer  and  away  from  the  older  in  Canada. 

If  we  stand  at  Milwaukee,  the  dip  is  eastward,  for  Mil- 
waukee is  on  the  Silurian,  and  eastward  we  have  the  Devon- 
ian and  Lower  and  Upper  Carboniferous  in  Michigan.  Lake 
Michigan  must  also  cover  a  portion  of  the  Silurian  and 
much  of  the  Devonian.  If,  on  the  contrary,  we  stand  at 


114  GEOLOGICAL  EXCURSIONS. 

the  St.  Clair  River,  the  dip  is  westward  on  the  same 
principle. 

Again,  if  we  stand  at  Sandusky,  Ohio,  we  are  on  the  Silu- 
rian ;  and  if  we  walk  straight  to  Cincinnati,  we  walk  a  long 
distance  on  Silurian,  and  then  come  to  Cambrian.  Then  if 
we  continue  our  travel  to  Nashville,  Tennessee,  we  pass 
again  over  Silurian,  a  narrow  belt  of  Devonian,  a  broad  belt 
of  Lower  Carboniferous,  and  then  come  to  a  very  narrow 
streak  of  Silurian  again  (too  narrow  to  show  on  the  map  at 
this  place,  though  it  can  be  seen  south  of  the  Cumberland 
River),  and  end  our  journey  on  the  Cambrian.  Should 
we  continue  southward  to  Mobile,  we  should  pass  off 
the  Cambrian  directly  upon  the  Lower  Carboniferous, 
which  extends  into  Alabama.  Then,  in  the  neighborhood 
of  Tuscaloosa,  we  should  pass  upon  the  Upper  Carbonifer- 
ous and  beyond  this  to  the  overlying  Cretaceous,  and  should 
find  Mobile  on  the  Tertiary. 

If  we  should  travel  from  Albany  to  Boston,  we  should 
start  on  Cambrian  rocks  and  pass  to  Silurian  rocks.  Before 
reaching  central  Massachusetts  we  should  pass  to  rocks 
which  are  not  fully  determined — perhaps  Cambro-Silurian, 
—  and  perhaps  also  an  outcrop  of  Eozoic.  Crossing  the 
valley  of  the  Connecticut,  would  be  found  Jura-Trias  rocks 
resting  horizontally  in  a  trough  excavated  in  the  older 
rocks.  Those  on  the  map  are  not  extended  far  enough 
north.  Beyond  this  valley  we  should  find  again  rocks 
which  are  perhaps  Cambro-Silurian.  Beyond  these  we 
should  have  Eozoic  rocks  for  the  greater  part  (all  Eozoic 


TO   THE   GEOLOGICAL   MAP.  115 

on  the  map)  until  reaching  Boston.     All  these  things  and 
a  thousand  others  may  be  studied  out  on  the  map. 

EXERCISES. 

If  you  travel  in  a  straight  line  from  Detroit  to  Milwaukee, 
what  systems  of  strata  will  you  pass  over?  What,  if  you  travel 
from  Mackinac  to  Cincinnati?  What,  between  Oswego  and 
Plattsburg?  What,  between  Charleston  and  Nashville?  State 
the  dip  of  every  system  of  strata  passed  between  St.  Louis  and 
Chicago.  Between  Duluth  and  Lake  Michigan.  Between  Sagi- 
naw  and  Springfield,  Illinois.  Between  Springfield  and  Cincin- 
nati. Between  Cleveland  and  Pittsburgh.  What  is  the  dip  of 
the  strata  at  Cleveland  ?  What,  at  Green  Bay  ?  What,  at  Bing- 
hamton,  New  York  ?  What,  at  Utica,  New  York  ?  Suppose  you 
bore  an  artesian  well  at  Lansing,  Michigan,  what  systems  of 
strata  will  be  passed  through  ?  What,  if  you  bore  at  Charleston, 
South  Carolina  ?  What,  if  you  bore  at  Hartford,  Connecticut  ? 
What,  if  you  bore  at  Peoria,  Illinois?  What,  if  you  bore  at 
Galveston,  Texas  ?  What,  if  you  bore  at  Montreal,  Canada  ? 
Would  an  artesian  well  bored  at  Cincinnati  pass  through  the  Silu- 
rian ?  Or  the  Devonian  ?  How  could  you  travel  from  Albany, 
New  York,  to  St.  Paul  without  passing  off  the  Cambro-Silu- 
rian?  How  from  Cairo  to  Cape  May  without  passing  off  the 
Tertiary?  How  many  great  patches  of  Upper  Carboniferous 
(Coal  Measures)  are  shown  on  the  map?  Into  what  states  does 
the  Appalachian  coal  area  reach  ?  Into  what  states,  the  Illinois 
coal  area  ?  Into  what,  the  Kansas  coal  area  ?  Into  what,  the 
Michigan?  Into  what,  the  Rhode  Island?  Which  state  has  the 
largest  area  of  Eozoic  rocks?  Which  next?  Which  has  the 
largest  area  of  Tertiary?  Which  state  contains  the  greatest 
number  of  different  systems  ?  Which  contains  the  fewest  dif- 
ferent systems?  What  states  have  the  largest  amount  of  soft 
rocks  ?  What  ones  have  most  Palaeozoic  rocks?  Give  the  names 
of  the  cities  indicated  by  black  dots  on  the  map,  and  state  what 
system  of  rocks  each  is  located  on. 


116  GEOLOGICAL   EXCURSIONS. 

EXCURSION  XXI.— To  the  Geological  Map. 
Geological  Sections. 

One  of  the  most  useful  things  for  a  student  of  geology 
is  to  take  exercises  on  the  geological  map.  One  object 
of  the  study  is  to  learn  the  geology  of  various  parts  of 
the  country.  You  must  not  look  merely  upon  the  flat 
surface  of  the  map.  It  is  not  enough  even  to  learn  the 
location  of  the  different  colors  lying  on  the  surface.  You 
must  think  of  each  color  or  system  of  markings  as  an 
outcropping  of  something  which  goes  down  beneath  the 
surface.  You  must  try  to  follow  it  beneath  the  surface  to 
some  other  region  where  it  outcrops  again.  You  must 
think  which  way  it  goes  beneath  the  surface  —  that  is,  what 
is  its  dip.  The  rule  already  given  determines  that.  So, 
when  you  look  on  the  geological  map  you  will  learn  to 
look  into  it,  and  far  beneath  the  surface.  You  will  then 
see  the  whole  solid  framework  of  the  rocks  which  underlie 
a  country. 

Now  we  shall  undertake  some  exercises  which  will 
give  us  the  power  of  penetrating  into  the  depths  of  the 
solid  crust.  With  the  geological  map  before  us,  we  will 
try  to  construct  some  geological  sections.  That  is,  if  we 
could  cut  straight  down  along  the  line  between  two  points 
which  may  be  selected,  to  the  depth  of  some  thousands  of 
feet,  and  then  look  at  the  cut  edges  of  the  strata,  what 
form  and  arrangement  would  they  present  to  us  ? 

To  begin  with  a  simple  case,  let  us  construct  a  section 
across  the  State  of  Michigan  from  Detroit  to  Grand  Haven. 


TO   THE   GEOLOGICAL   MAP.  117 

We  will   first  draw  a  line  G  D,  Figure   38,   to  represent 
the  distance  along  the  surface  between 

__  G(jc        b       a  D 

the  two  points.      We  suppose  ourselves         — "-• ' — 

FiG.38.— PREPARING  FOB 

facing  north.  We  notice  that  Detroit  A  GEOLOGICAL  SEC- 
stands  on  the  Devonian.  Take  the 
distance  from  Detroit  to  the  western  border  of  the  Devo- 
nian, and  lay  it  off  from  D  on  the  line  G  D.  This  distance 
extends  to  a.  Next,  lay  off  from  a  the  distance  which 
corresponds  to  the  breadth  of  the  Lower  Carboniferous  in 
the  direction  from  Detroit  to  Grand  Haven.  This  stretches 
to  b.  Thirdly,  lay  off  the  distance  which  our  route  passes 
over  the  Upper  Carboniferous.  This  takes  us  to  c. 
Fourthly,  lay  off  the  distance  to  the  western  border  of 
the  Lower  Carboniferous ;  this  takes  us  to  d.  Finally, 
lay  off  the  short  distance  to  Grand  Haven  on  the  border 
of  Lake  Michigan.  This  takes  us  to  G. 

Next,  we  have  to  consider  what  is  the  dip  of  the  strata 
at  each  point.     On  our  principles,  the  dip  is  toward  the 
Upper  Carboniferous  from  both  ends  of  the  line.     Draw 
lines  down  obliquely,  according  to  the 
dip,  from  «,  £,  c  and  d,  Figure  39,  the 
boundary    points    between    the    forma- 

FIG.  39.  —  PROGRESSING 

tions.     Then,  knowing  that  the  Lower        WITH  A  GEOLOGICAL 

SECTION. 

Carboniferous,  which  dips  down  west- 
ward in  the  eastern  part  of  the  state,  is  the  same  which 
comes  up  to  the  surface  from  the  eastward,  in  the  western 
part  of  the  state,  we  can  connect  the  lines  representing 
the  lower  and  upper  surfaces  of  this  system.  That  is, 
the  upper  line  will  extend  from  b  to  <?,  passing  down  under 


118  GEOLOGICAL   EXCURSIONS. 

the  Upper  Carboniferous;  and  the  lower  line  will  extend 
from  a  to  d,  passing  under  both  Upper  and  Lower  Car- 
boniferous. The  dip  of  the  strata  from  D  must  pass  in  the 
same  direction  as  from  a  and  £.  But  notice  that  Detroit 
is  not  on  the  eastern  limit  of  the  Devonian.  The  line  from 
the  eastern  limit — wherever  it  is  —  will  pass  some  distance 
under  Detroit,  as  at  e.  We  need  not  know  where  it  comes 
up  to  the  surface.  It  is  somewhere  to  the  eastward,  but 
we  may  cut  it  off  at  6,  as  we  are  only  required  to  construct 
the  section  to  Detroit.  That  line,  then,  ending  at  0,  shows 
the  bottom  of  the  Devonian.  Passing  westward  it  will 
come  up  at  the  west  side  of  the  Devonian,  wherever  that  is. 
But  the  first  system  west  of  Lake  Michigan  is  the  Silurian, 
and  the  place  for  the  bottom  of  the  Devonian  is  between 
it  and  d,  near  Grand  Haven.  The  western  outcrop  of  the 
bottom  of  the  Devonian  seems  to  be  in  the  bottom  of  Lake 
Michigan.  This  belief  is  confirmed  by  observing  that  on 
the  map,  the  outcrop  of  the  Devonian  strikes  the  south 
end  of  Lake  Michigan  and  seems  to  pass  under  the  lake. 
It  comes  mostly  from  under  the  lake  again  in  the  region 
of  Grand  Traverse  and  Little  Traverse  Bays  and  Mackinac. 
We  will  therefore  assume  that  the  western  outcrop  of  the 
Devonian  is  under  the  lake.  We  will  also  draw  a  little 
depression  to  represent  the  bed  of  the  lake. 

So  far  we  have  assumed  that  the  surface  is  a  dead  level 
from  Detroit  to  Grand  Haven ;  but  if  we  happen  to  know 
that  the  centre  of  the  state  swells  up  a  little,  we  should 
so  represent  it.  We  ought,  indeed,  to  know  this  ;  because 
if  you  look  on  any  map  of  Michigan  you  see  the  streams 


TO   THE   GEOLOGICAL   MAP. 


119 


all  flowing  from  the  interior  into  the  surrounding  lakes. 
If,  then,  we  show  the  surface  configuration,  our  section 
will  be  a  geological  profile.  Here  it  is,  in  Figure  40,  but 


FIG.  40.  —  COMPLETED  GEOLOGICAL  SECTION  BETWEEN  DETROIT  AND 

HAVEN,  MICH. 


on  a  scale  twice  as  large.  In  completing  the  section  we 
may  bear  in  mind  that  the  Silurian  which  outcrops  at 
Milwaukee  passes  under  Lake  Michigan  and  the  state  of 
Michigan,  and  we  may  so  represent  it,  though  a  section 
across  Michigan  does  not  require  this.  It  would  be 
proper  also  to  represent  the  Cambrian  under  the  Silu- 
rian, since  we  see  from  the  map  that  on  the  west  of  Mil- 
waukee it  passes  eastward  under  the  Silurian.  And, 
finally,  we  notice  that  in  central  Wisconsin  the  Eozoic 
passes  southward  under  the  Cambrian  ;  and  we  may  fairly 
assume  that  it  would  appear  beneath  the  Cambrian  under 
Michigan'  if  we  were  able  to  make  actual  examination.  So 
we  fill  in  the  lower  left-hand  corner  of  our  section  with  the 
marks  indicating  Eozoic.  Now  the  section  is  complete. 

We  have,  in  fact,  extended  the  section  farther  west  than 
was  required.  We  might  have  cut  it  off  at  Grand  Haven. 
Also,  we  have  carried  it  deeper  than  necessary.  All  that 
is  essential  in  a  section  from  Detroit  to  Grand  Haven  is 
shown  by  the  broken  lines. 


120  GEOLOGICAL  EXCUKSIONS. 

Next,   let   us   construct   a  geological   section   from   the 

Eozoic  north  of  Lake  Ontario  to  William  sport  on  the  Coal 

Measures  of  Pennsylvania ;   and  let  us  suppose  ourselves 

facing  east.     Draw  a  line  E  W,  Figure  41,  to  represent  the 

length  of  the  section.     Then,  allowing  a 

1-4 — ' — H~l — '~^H       little   space   to   the   right  of  E  for  the 

FIG.  41  .—PREPARING  FOR 

A  GEOLOGICAL  SEC-  distance  to  the  southern  margin  of  the 
Eozoic,  fix  on  a  point  a,  for  the  border 
of  the  Cambrian.  The  dividing  line  between  the  Cam- 
brian and  Silurian  is  under  the  lake ;  let  us  locate  it  under 
£.  The  southern  limit  of  the  Silurian  will  be  at  c.  The 
southern  limit  of  the  Devonian  will  be  at  d\  and  here  the 
Lower  Carboniferous  begins.  The  southern  limit  of  the 
Lower  Carboniferous,  which  is  the  northern  limit  of  the 
Upper  Carboniferous,  will  be  at  e.  Then  the  southern 
extremity  of  our  section  will  be  at  W,  just  over  the  border 
of  the  Coal  Measures. 

Now,  we  understand  that  all  these  rocks  dip  southward. 
So  we  draw  lines  from  the  points  #,  5, 


KxAJ^  VjX^j        c->  d->  e->  Figure  42,  to  represent  the  dip, 


-^x|       and  terminate  them  at  such  points  as  to 

FIG.  42.— PROGRESSING  n 

WITH  A  GEOLOGICAL     produce  a  neat  ngure  showing  all  that 
is  required.     Then  we  may  fill  in  with 
the  lines  and  characters  chosen  to  represent  the  various 
systems. 

Notice  that  it  is  customary  to  represent  the  dip  some- 
what greater  than  the  reality,  especially  when  the  real  dip 
is  but  slight.  Notice,  also,  that  this  makes  the  thicknesses 
of  the  formations  too  great  to  be  in  due  proportion  to  the 


TO  THE   GEOLOGICAL   MAP. 


121 


distances    along  the   surface.     All    this   is   only  for  con- 
venience. 

We  have  constructed  this  section  thus  far  on  the 
assumption  of  a  dead  level  from  end  to  end.  But  we 
ought  always  to  represent  the  relative  elevations  of  dif- 
ferent points  as  well  as  we-  can.  In  fact,  geologists  often 
take  very  great  pains  to  ascertain  the  levels  of  different 
points.  If  the  region  where  E  is  located  is  somewhat  ele- 
vated, we  should  so  represent  it.  And  if  we  know  that  a 
high  bluff  of  strata  extends  along  the  south  shore  of  Lake 
Ontario,  we  should  so  represent  that.  An  improved  sec- 
tion between  the  two  points  would  be  as  shown,  Figure 
43.  This  is  made  on  a  scale  four  times  as  large  as  the 
other,  which  is  too  small  for  convenience.  Here  we  notice 
a  slope  from  north  and  from  south  toward  Lake  Ontario. 


E 


FIG.  43.— COMPLETED  GEOLOGICAL  SECTION. 
E,  Canadian  Eozoic.    Co,  Coburg.    R,  Rochester.    C,  Corning.    W,  Williamsport. 

Also  a  slope  from  both  directions  toward  the  Chemung 
Kiver.  These  things  are  not  all  shown  by  the  map;  but 
if  you  can,  in  any  way,  obtain  information  about  the  con- 
figuration of  the  surface,  that  should  be  introduced  into 
your  section.  You  will  often  have  to  refer  to  your  geo- 
graphical atlas  to  learn  where  places  mentioned  are 
located.  The  directions  in  which  the  streams  run  will 


122  GEOLOGICAL  EXCURSIONS. 

also  show  you  what  regions  are  more  elevated,  and  what 
are  less  elevated. 

The  following  is  the  way  we  complete  the  geological 
profile.  Having  laid  down  the  necessary  points  along  a 
horizontal  line  A  B,  draw  vertical  lines  from  these  points, 
as  shown,  Figure  43,  and  draw  as  exactly  as  you  can  a 
line  E  P,  to  represent  the  surface  of  the  earth.  The  points 
a,  c,  d,  e,  where  this  line  intersects  the  vertical  lines,  indi- 
cate the  bounds  of  the  different  formations.  From  these 
points  we  may  draw  lines  to  represent  the  dip  and  the 
thickness  of  each  formation. 

You  ought  to  take  a  great  deal  of  exercise  on  the  Geo- 
logical Map,  and  especially  in  the  construction  of  sections. 
No  matter  if  it  requires  two  or  three  days  to  finish  one 
Excursion. 

Let  us  construct  a  section  from  Nashville  to  Savannah. 
Here  it  is  (Figure  44).  You  will  notice  that  the  Cambrian 


FIG.  44.— SECTION  FROM  NASHVILLE  TO  SAVANNAH  AND  TH-E  ATLANTIC 

OCEAN. 

east  of  Nashville  is  not  known  to  be  overlaid  by  Silurian; 
and  when  we  trace  it  to  the  east  of  the  Appalachians  it 
is  so  metamorphosed  that  we  are  unable  to  say  whether 
it  is  Cambrian  or  Silurian,  and  so  it  is  simply  put  down 
on  the  map  as  Cambro-Silurian.  After  passing  the  dome 
of  Eozoic  we  find  it  overlaid  directly  by  Tertiary  strata, 


TO   THE    WHITE   MOUNTAINS.  123 

and  we  must  so  represent.  Not  unlikely,  however,  some 
strata  intermediate  in  age  between  Eozoic  and  Tertiary 
would  be  found  beneath  the  Tertiary  if  we  could  make 
exploration.  The  Tertiary  passes  under  the  waters  of  the 
Atlantic. 

EXERCISES. 

Construct  sections  as  follows:  From  Madison,  Wis.,  to  Chi- 
cago. From  Chicago  to  St.  Louis.  From  Sandusky,  Ohio,  to 
Nashville,  Tenn.  From  Mackinac  to  Cincinnati.  From  Montreal 
to  Albany.  From  New  York  City  to  Oswego.  From  St.  Louis 
to  Cincinnati.  From  Cincinnati  to  Newbern,  N.  C.  From  St. 
Paul  to  Chicago.  From  Cairo,  111.,  to  Cincinnati.  From  Kings- 
ton, Out.,  to  Chicago.  From  Detroit  to  Fortress  Monroe.  From 
Cleveland  to  Cincinnati,  and  thence  down  the  Ohio  to  its  mouth. 


EXCURSION   XXII.— To  the  White  Mountains. 
The  Eozoic  Bocks. 

You  ought  now  to  study  a  little  more  particularly  the 
different  systems  of  rocks  which  you  see  indicated  on  the 
geological  map  of  the  country.  We  will  begin  with  the 
Eozoic.  Glancing  at  the  map,  you  perceive  that  the  largest 
region  where  Eozoic  rocks  come  to  the  surface  is  north  of 
the  United  States,  but  sending  extensions  southward  into 
Wisconsin  and  New  York.'  You  see  also  indications  of 
the  Eozoic  in  Maine,  N"ew  Hampshire,  Massachusetts  and 
Rhode  Island.  There  is  also  an  extensive  area  along  the 
eastern  flanks  of  the  Appalachians.  There  are  smaller 
areas  at  New  York  City,  in  Dakota,  Missouri,  the  Indian 


124  GEOLOGICAL   EXCURSION'S. 

Territory  and  Texas.  In  the  western  part  of  the  country 
are  many  other  patches  large  and  small ;  but  these  are  not 
included  in  our  map. 

We  could  obtain  good  views  of  the  Eozoic  rocks  by 
visiting  any  of  these  regions.  The  most  convenient  for 
most  of  us  are  the  Eozoic  rocks  lying  to  the  north.  From 
these  came  the  boulders  which  overstrew  all  the  region 
south  of  the  Eozoic  down  to  the  latitude  of  Cincinnati  — 
the  boulders  whose  different  sorts  we  have  so  much  studied. 
If  we  visit  the  Eozoic  regions,  we  shall  find  the  same  kinds 
of  rocks  as  bed-rocks ;  and  we  shall  find  them  exposed  at 
the  surface  in  very  many  places. 

Suppose  ourselves  in  the  region  of  the  White  Mount- 
ains. We  visit  the  Glen  House  on  the  east  of  Mt.  Wash- 
ington, and  on  each  side  of  us  rise  the  lofty  rounded  forms 
which  are  characteristic  of  the  Eozoic.  In  front  is  the 
stupendous  "Presidential  Range,"  with  the  bald  summits 
of  Mts.  Madison,  Adams,  Jefferson,  Clay,  Washington, 
Monroe,  Franklin,  Pleasant,  Clinton  and  Webster  rising 
before  us  —  most  of  them  in  sight  together.  In  the  rear 
of  the  Glen  House  rise  the  similarly  bald  and  rounded 
summits  of  the  " Carter  Range."  If  we  go  to  the  top  of 
Mt.  Washington  and  look  down  on  the  country  for  fifty 
miles  in  every  direction,  it  seems  to  be  a  dark  swelling 
mass  of  mountain  tops,  nearly  all  of  like  shape.  This  is  a 
good  illustration  of  the  style  of  weathering  which  crystalline 
rocks  undergo.  Granitic  and  gneissic  regions  seldom  pre- 
sent the  pointed  or  angular  features  often  shown  by  strata 
belonging  to  some  of  the  other  systems. 


TO   THE   WHITE    MOUNTAINS. 

Here  is  a  view  of  Mt.  Kearsarge,  one  of  the  White 
Mountains,  showing  the  rounded  forms  of  the  summits. 
(Figure  45.)  There  are  some  large  boulders  in  the  fore- 
ground. In  contrast  with  this  I  present  you  next  a  view  of 
pinnacled  mountains,  such  as  exist  when  their  summits  are 
formed  of  schists  turned  up  on  edge.  The  summits  formed 


FIG,  45. — MT.  KEARSARGE  AMONG  THE  WHITE  MOUNTAINS,  SHOWING  ROUNDED 
SUMMITS.     BOULDERS  IN  THE  FOREGROUND.     (Photograph.) 

of  massive  rocks  like  granite  are  evenly  eroded  by  weather- 
ing, and  result  generally  in  smoothly  rounded  forms,  while 
summits  formed  of  schists  turned  on  edge  are  eroded  deep- 
est in  the  spaces  between  the  hardest  strata,  and  this  leaves 
the  hardest  strata  projecting.  Such  summits  are  called 
" needles"  in  Switzerland.  (See  Figure  46.)  Some  of  the 


126 


GEOLOGICAL   EXCURSIONS. 


"White  Mountain  summits   present   pinnacled  forms   for  a 
similar  reason.     Mt.  Chocorua  is  a  pretty  good  example. 


FIG.  46. —  THE  NEEDLES  OF  CHARMOZ  AND  THE  MER  DE  GLACE. 

Now  let  us  view  these  massive  and  schistose  rocks  a 
little  more  closely.  You  will  be  amazed  to  see  how  they 
have  been  upturned  and  folded.  Often  the  strata  stand 
almost  vertically  on  their  edges ;  and  they  are  often  crum- 


FIG.  47. —  SECTION  THROUGH  MT.  KEARSARGE,  N.  H. 

Wilmot.    W  H,  Wilmot  House.    Wh  H,  White  House.    P,  Plumbago  Pt.    a,  Porphy- 
ritic  Gneiss.    6,  Andalusite  Mica  Schist,    c1,  Granite. 


TO   THE    WHITE   MOUNTAINS. 


127 


Ss 


pled  like  a  pocket  handkerchief. 
You  see  this  constantly  in  ascend- 
ing Mt.  Washington.  I  would  be  .»  g 

o 

glad  to  show  you  a  section  through  »   £ 

this  mountain,  but  it  has  not  yet  g   ^ 

been    thoroughly   worked  out  by  *   g 

geologists.     Here  (Figure   47)   is  ^  fe    ,•; 

a  section,   however,  through  Mt.  g  ^  \\ 
Kearsarge,  the  same  whose  summit 
contour  you  have  seen.     It  rises 

in  southeastern  New  Hampshire,  gf «   | 

and  has  been  carefully  studied  by  |^  | 

Professor   C.    H.    Hitchcock.     It  f  |  § 

shows  how  wonderfully  the  great  «  o  g 

masses   of  the   rocks   have  been  1 1  ^  -• 

folded,  and  afterward  worn  down.  |  »•  g 

P*  <* 

The  dotted  lines  indicate  the  sup-  ^  a  & 

A  J~   *^       O 

posed  former  extent  of  the  strata.  |  3   o  ** 
Next,  in  Figure  48,  you  have 

<D        3 

a    carefully    investigated    section  |.  o 

through  the  Eozoic  rocks  of  Can-  ^  g 

ada,  worked  out  by  Sir  William  g   ^ 

Logan.      The    first    thing   which  K  5 

impresses  you  is  the  wonderfully  f  -^ 

o     o 

wrinkled  condition  of  the  strata.  §.  ^ 

The  dotted  lines  are  intended  to  ^  g 

show  the   connections  of   strata.  | 

So  you  see  also  evidence  of  a  vast 

amount  of  erosion.     Notice  here  further  the  great  limestone 


^^  Porphyry 


128  GEOLOGICAL   EXCUKSIONS. 

masses.     In  the  upper  one  of  these  are  found  relics  of  the 
first  animals  which  ever  lived  on  our  planet. 

Next   follows    a    section    through    the    Eozoic    rocks  of 
Wisconsin.     Here  you  see  the  two  u systems"  into  which 

Laurentian  •         Huronian  Cambrian 


FIG.  49. — SECTION  ACROSS  THE  ROCKS  OF  WISCONSIN.     (Chamberlin.) 

1.  Potsdam  Sandstone.  2.  Lower  Magnesian  Limestone.  3.  St.  Peter's  Sandstone.  4. 
Trenton  Limestone.  5.  Galena  Limestone.  6,  Cincinnati  Shales.  7.  Niagara 
Limestone.  8.  Lower  Helderberg  Limestone.  9.  Hamilton  Limestone. 

the  Eozoic  is  divided  —  the  Laurentian  below  and  the 
Huronian  above.  This  section  extends,  toward  the  right, 
through  the  other  rocks  of  Wisconsin,  which  we  shall 
speak  of  hereafter.  The  Laurentian  here  and  elsewhere 
shown  is  composed  of  great  masses  of  granites,  gneisses 
and  schists,  and  in  some  regions  includes  great  beds  of 
crystalline  limestone,  or  marble.  Much  of  the  marble 
of  this  continent  is  from  the  Laurentian.  The  Huronian 
System  of  Rocks  is  composed  chiefly  of  diorites,  dia- 
bases, quartzites,  slates  and  conglomerates.  Great  beds 
of  iron  ore  are  found  both  in  the  Laurentian  and  the 
Huronian.  They  occur  in  masses  between  beds  of  other 
rocks,  and  generally  swell  out  to  greatest  thickness  in  the 
middle,  and  taper  off  at  each  extremity.  This  may  be 
distinctly  seen  in  the  Marquette  Iron  Region.  At  Pilot 
Knob  in  Missouri,  however,  in  the  Penokie  Range  of 
Wisconsin,  and  many  other  regions,  the  iron  ore  forms 
thick  strata,  which  present  a  structure  similar  to  that  of  the 


TO   THE    WHITE    MOUNTAINS. 


129 


strata  above  and  below.  Figure  50  is  a  section  across  the 
eastern  portion  of  the  Penokie  Eange.  Here  the  massive 
Laurentian  granites,  gneisses  and  schists,  L,  are  unconform- 
ably  overlaid  by  the  Huronian  slates,  iron-schists,  quartz- 
ites  and  diorites,  H.  These  are  succeeded  by  the  "  South 
Range"  of  copper-bearing  rocks  (Kewenian),  C,  consisting 
of  various  bedded  dolerites,  with  alternating  beds  of  sand- 
stones and  conglomerates.  Still  farther  north  are  the  hori- 
zontal sandstones  of  Cambrian  age.  The  iron  ores  of 
Northern  JSTew  York,  and  of  many  other  parts  of  the  world, 
are  found  in  rocks  belonging  to  the  Eozoic  System. 


FIG.  50. — SECTION  THROUGH  AN  IRON  RANGE  IN  WESTERN  MICHIGAN,  BE- 
TWEEN LAKE  GOGEBIC  AND  MONTREAL  RIVER,  SHOWING  POSITION  OF  THE 
IRON  ORE,  AND  THE  RELATIONS  OF  FOUR  SYSTEMS  OF  ROCKS.  (Pumpelly 
and  Brooks.) 

As  these  Eozoic  rocks  are  seen  everywhere  to  pass 
under  all  the  other  rocks,  they  must  have  been  formed 
before  the  others.  The  Eozoic  rocks  are  thought  to  be 
not  less  than  fifty  thousand  feet  in  thickness.  And  we  hold 
that  they  were  originally  sediments  in  the  bottom  of  the 
sea.  All  this  indicates  that  a  vast  length  of  time  must 
have  been  occupied  in  laying  down  sufficient  sediments  to 
form  the  Eozoic  and  all  the  other  rocks.  It  would  seem, 
then,  that  this  world  has  had  a  history,  and  a  very  long 


130  GEOLOGICAL   EXCURSIONS. 

history.  We  have  to  think,  therefore,  of  the  periods  of 
time  spent,  as  well  as  of  the  work  done.  As  the  whole 
work  is  divided  into  Systems  and  Great  Systems  of  strata, 
so  the  whole  time  is  divided  into  Ages  and  Eras  of  time. 
This  is  indicated  in  the  Geological  Column,  Figure  29. 

If  the  racks  which  make  the  White  Mountains  were  at 
first  sediments  in  the  bottom  of  the  ocean,  and  are  now 
five  or  six  thousand  feet  above  the  surface  of  the  ocean, 
it  is  plain  that  the  old  sediments  must  have  been  upraised 
to  the  extent  of  a  mile  or  two.  Who  can  imagine  the 
power  necessary  to  lift  up  the  whole  mass  of  the  White 
Mountains?  Then  consider  the  attitudes  in  which  the 
strata  stand.  Look  again  at  the  section  of  Mt.  Kearsarge 
and  trace  the  dotted  lines.  They  are  intended  to  show 
how  the  different  strata  seem  to  have  been  once  connected 
together.  The  solid  rocks  have  been  folded  and  over- 
lapped, as  if  soft  as  molasses  candy.  What  power  could 
mould  the  substance  of  mountains  into  such  shape  ?  Look 
again,  also,  at  the  Canada  and  Wisconsin  sections,  and  note 
the  wonderful  crumpling  of  the  strata.  These  rocks  are 
solid  and  massive  granites,  syenites,  quartzites,  diabases 
and  schists.  Plainly,  the  forces  which  could  do  such  work 
are  inconceivably  vast.  These  things  lead  us  to  cast  our 
thoughts  backward  over  the  world's  long  history.  What 
changes  have  taken  place  since  the  White  Mountains  were 
soft  mud  in  the  bottom  of  the  sea!  Indeed,  we  are  just 
getting  glimpses  of  the  world's  grand  history.  It  is  the 
business  of  geology  to  study  these  things,  and  find  out,  as 


TO   THE    UPPER    MISSISSIPPI.  131 

far  as  possible,  what  has  been  the  nature  of  the  events 
which  have  made  up  the  history  of  our  planet. 

EXERCISES. 

Is  there  any  connection  between  the  Eozoic  of  Wisconsin 
and  the  Eozoic  of  Missouri  ?  Has  it  ever  been  proved  that  the 
Eozoic  exists  underground  in  regions  where  it  does  not  appear  at 
the  surface  ?  In  boring  to  a  great  depth,  how  would  we  know 
when  Eozoic  rocks  are  reached?  Do  you  think  an  artesian  well 
likely  to  be  found  in  Eozoic  rocks?  If  not,  why  not?  Were 
the  first  animals  land  or  water  animals  ?  Were  they  fresh-water 
or  marine  animals?  Would  you  expect  them  to  be  high  or  low 
in  rank  ?  What  is  the  reason  why  the  Adirondack  mountains 
have  no  Cambrian  strata  over  them?  When  you  find  Eozoic 
rocks  exposed,  can  you  feel  certain  that  no  strata  ever  covered 
them?  Look  at  the  Eozoic  in  Georgia;  is  there  any  reason  to 
suppose  the  Cambro-Silurian  ever  extended  any  farther  south- 
east ?  How  is  it  possible  that  Cambro-Silurian  rocks  ever  lay 
between  the  Eozoic  and  the  Tertiary  in  Georgia?  Could  such 
rocks  have  been  swept  away  in  some  age  before  the  Tertiary 
were  laid  down  ?  What  system  of  rocks  appears  on  Manhattan 
island?  Are  the  artesian  wells  in  Brooklyn  bored  into  Eozoic 
rocks  ? 


EXCURSION  XXIII.— To  the  Upper  Mississippi. 
Cambrian  (or  Lower  Silurian)  Rocks  and  History. 

By  looking  over  our  little  geological  map,  you  notice 
several  regions  covered  by  the  lines  which  indicate  Cam- 
brian or  Lower  Silurian.  One  of  the  largest  of  these 
regions  covers  much  of  Wisconsin  and  Minnesota — on  both 
sides  of  the  Mississippi  River,  and  stretches  eastward  through 
northern  Michigan  and  the  Manitoulin  islands.  Another 


132 


GEOLOGICAL   EXCURSIONS. 


stretches  along  the  north  side  of  Lake  Ontario,  and  across 
northern  New  York  into  Vermont,  New  Hampshire  and 
Massachusetts.  Another  region  is  in  southern  Ohio  and 
northern  Kentucky  ;  and  within  this  are  the  cities  of 
Cincinnati,  Lebanon,  Madison  and  Richmond,  Ind.,  and 
Frankfort  and  Lexington,  Ky.  Another  region  is  in  Ten- 
nessee, and  this  embraces  Nashville,  Lebanon,  Columbia 
and  Franklin.  Still  another  extensive  region  stretches 


FIG.  51. — BLUFFS  ON  THE  UPPER  MISSISSIPPI. 
(D.  D.  Owen.) 


CAMBRIAN  ROCKS. 


along  the  east  side  of  the  Appalachian  mountains.  You 
should  trace  out  the  boundaries  of  each  of  these  Cambrian 
regions,  and  see  what  states  and  provinces  they  partly  cover, 
and  what  cities  are  included  in  them.  To  do  this  you  will 
have  to  study  also  the  common  school-atlas  ;  but  it  will  be 
very  interesting  and  profitable. 

You  would  be  delighted  to  visit  any  of  these  regions  and 
see  what  kind  of  rocks  the  Cambrian  rocks  are — how  much 


TO   THE    UPPER    MISSISSIPPI.  133 

less  hard  they  are  than  the  Eozoic  rocks,  and  how  much  less 
tilted  and  crumpled.  You  would  wonder  also  at  the  strange 
forms  of  the  fossils  in  the  rocks — that  is,  the  shells  and 
other  remains  of  animals  which  lived  in  the  sea  when  these 
rocks  were  soft  sediments  accumulating  on  the  bottom.  Let 
us  first  go  to  the  Upper  Mississippi.  If  we  ascend  the 
river  by  steamer  to  St.  Paul,  we  shall  see  high  rocky  bluffs 


FIG.  52. — "HORNETS'  NEST,"  Wis.      EROSION  OF  CAMBRIAN  ROCKS. 
(Chamberlin.) 

rising  along  one  shore  or  the  other,  and  sometimes  on  both 
shores,  most  of  the  way  from  Prairie  du  Chien.  The 
upper  portion  of  the  bluff  is  generally  a  rusty  irregular 
magnesian  limestone,  while  below  this  lies  a  great  sandstone 
formation.  Figure  51  shows  the  appearance  of  these  bluffs 
at  many  places.  Here  are  evidently  two  ledges  or  forma- 
tions of  strata,  and  a  great  amount  of  earth  has  accumulated 


134 


GEOLOGICAL   EXCURSION'S. 


at  the  foot  of  eacli  ledge,  almost?  burying  it  out  of  sight. 
This  earth  has  resulted  largely  from  the  disintegration  of 
the  rocks.  The  lower  ledge  here  is  the  great  sandstone,  and 
the  next  is  the  magnesian  limestone.  In  many  places  these 
formations  are  less  buried,  and  we  have  high  vertical  cliffs 
of  buff  sandstone  and  limestone  as  shown  in  Figure  23. 
The  strata  shown  in  Figure  22  are  sandstone  of  the 
same  age. 

The  weathering  of  these  rocks  in  Wisconsin  and  Minne- 
sota has  resulted  in  many  remarkable  forms.  Figure  24  is 
an  example  ;  and  Figure  52  is  another.  Here  the  underlying 
sandstone  weathers  away,  and  leaves  the  more  durable 
magnesian  limestone  overhanging.  In  other  cases,  enor- 
mous towers  are  left 
standing  in  the  midst  of 
a  plain,  showing  how  ex- 
tensively formations  have 
been  swept  away.  Fig. 
53  is  an  example  of  this 
kind  in  Dakota  county, 
Minn.  Here  the  isolated 
column  is  over  19  feet 
high  above  the  base, 
which  is  itself  25£  feet 

FIG.  53.— "CASTLE  ROCK,"  MINN.  OUT-  high?  making  the  whole 
LIER  OF  CAMBRIAN  ROCKS.  (Photo-  outlier  44  feet  7  inches 
graph.)  . 

above  the  sandy  plain. 

As  we  ascend  the  river,  these  formations  gradually  lower. 
"When  we  reach  Fort  Snelling  near  St.  Paul,  we  see  a  white 


TO  THE   UPPEK   MISSISSIPPI.  135 

sandstone  formation  on  the  top  of  the  magnesian  limestone, 
and  rising  vertically  from  the  water.  It  may  really  be  found 
at  the  top  of  the  bluff  most  of  the  way  from  Mac  Gregor. 
In  Figure  51  is  an  indication  of  it  in  a  third  terrace.  This 
sandstone  \&  friable  ^  that  is,  it  easily  crumbles  to  pieces.  It 
is  called  the  St.  Peter's  Sandstone,  while  the  lower  one  is 
the  Potsdam  Sandstone. 

When  we  go  back  from  the  river  to  the  Falls  of  Minne- 
haha  near  Fort  Snelling,  we  find  a  limestone  formation  still 
higher  in  the  series.  This  extends  to  St.  Paul,  and  makes 
the  high  limestone  bluff  there  and  at  Minneapolis.  It  is 
called  the  Trenton  Limestone.  The  Falls  of  St.  Anthony  at 
Minneapolis  are  caused  by  a  precipice  in  the  Trenton  Lime- 
stone. All  these  great  formations  together  make  up  what  is 
called  the  Cambrian  or  Lower  Silurian.  Here  are  the  names 
in  regular  order  above  the  Eozoic  : 

f  Trenton  Limestone. 

St.  Peter's  Sandstone. 
CAMBRIAN  SYSTEM    \ 

|  Lower  Magnesian  Limestone. 

[  Potsdam  Sandstone. 
Eozoic  GREAT  SYSTEM. 


a  a  a  b 

FIG.  54. — SECTION  ALONG  THE  VALLEY  OF  THE  UPPER  MISSISSIPPI.  CAMBRIAN 
ROCKS,  a.  Eozoic  rocks,  b.  Potsdam  Sandstone,  c.  Lower  Magnesian 
Limestone,  d.  St.  Peter's  Sandstone,  e.  Trenton  Limestone. 

And  here  is  a  diagram  or  ideal  section  along  the  Upper 
Mississippi   showing   how   these   formations    succeed   each 


136 


GEOLOGICAL   EXCURSIONS. 


other.  Notice  the  Eozoic  system  of  rocks  at  the  bottom. 
They  are  much  more  disturbed  than  the  Cambrian  above, 
and  are  much  contorted.  A  difference  in  the  dip  between 
two  formations,  such  as  you  see  here,  is  called  an  uncon- 
formability.  This  is  illustrated  also  in  Figures  49  and  50. 
Notice  also,  the  irregularity  of  the  surface  of  the  Eozoic 
rocks.  It  looks  as  if  they  had  been  extensively  worn  away 
before  the  Potsdam  Sandstone  was  deposited  upon  them. 
This  shows  that  a  long  interval  of  time  passed  after  the 
Eozoic  rocks  were  formed  and  disturbed,  before  the  epoch 
of  the  Potsdam  began.  Then  the  Potsdam  sands  were  laid 
down  in  nearly  horizontal  beds,  accumulating  most  deeply  in 
the  hollows  of  the  Eozoic.  In  this  way  the  thickness  of  the 
Potsdam  Sandstone  is  very  variable.  Figure  49,  across 
the  rocks  of  Wisconsin,  shows  some  of  the  same  things. 

Notice  also,  how  the  upper  surface  of  the  Magnesian 
Limestone  is  worn  down  irregularly.  Here  also,  the  over- 
lying sandstone  presents  a  very  variable  thickness.  So 
there  is  a  ~break  also  between  these  two  formations,  though 
we  discover  no  discordance  in  their  dips. 

Now  I  will  show  you  another  section  through  these  rocks 


FIG.  55. — SECTION  IN  SAUK  Co.,  Wis.  (Chamberlin.)  B.  Baraboo  River. 
D.  Devil's  Nose.  W.  Wisconsin  River,  separating  Sank  from  Columbia 
Co.  a.  North  Quartzite  Range,  b.  South  Quartzite  Range,  d.  Pots- 
dam Sandstone,  e.  /.  Upper  portions  of  Potsdam  Sandstone,  g.  Low- 
er Magnesian  Limestone,  h.  Drift. 


TO    THE    UPPER    MISSISSIPPI.  137 

—  a  real  section,  studied  out  by  the  geologists  of  Wisconsin. 
It  is  very  remarkable.  See  Figure  55.  The  Eozoic  beds 
here  exposed  are  Huronian  quartzite.  How  surprisingly 
irregular  their  upper  surface!  How  the  knobs  of  quartzite 
protrude!  On  this  wasted  knobby  surface  the  sands  were 
deposited  which  make  the  Potsdam  formation.  Toward  the 
right  (south)  we  cannot  see  the  bottom  of  the  Potsdam.  In 
other  places  the  Eozoic  rises  quite  above  the  upper  surface 
of  the  Potsdam.  But  the  Potsdam  itself  has  also  been 
enormously  eroded,  or  worn  away,  since  the  time  when  it 
was  first  completed.  See  how  it  clings  to  the  slopes  of  the 
South  Quartzite  Range.  These  clinging  masses  seem  to  be 
the  ends  of  strata  which  once  extended  a  great  distance. 
These  same  strata  are  preserved  also,  in  the  lower  portions 
of  the  singular  towers  which  appear  at  the  right  of  the 
section.  These,  like  the  tower  in  Figure  53,  are  remnants 
of  vast  sheets  of  sandstone  and  limestone  which  were  once 
unbroken  and  continuous  over  a  large  part  of  Wisconsin 
and  Minnesota.  Such  outlying  remnants  of  a  formation  are 
called  outliers.  So  it  appears  that  the  present  surface  has 
been  extensively  eroded.  How  precisely  it  resembles  those 
ancient  surfaces  at  the  top  of  the  Lower  Magnesian  Lime- 
stone and  the  top  of  the  Eozoic.  How  plainly  these  things 
teach  us  that  after  the  close  of  the  Eozoic  there  was  a  land 
surface  for  a  long  time,  which  wasted  away  quite  like  our 
present  surface,  and  then  the  ocean  overflowed  again  and 
deposited  the  sands  which  afterward  became  consolidated  in 
the  Potsdam  Sandstone.  And  the  ocean  continued  till 
the  Magnesian  Limestone  was  deposited.  Then  the  surface 


138  GEOLOGICAL   EXCURSIONS. 

of  this  was  dry  land  again,  and  another  long  period  of 
erosion  followed.  Then  the  ocean  came  still  again  and 
deposited  the  clean  sand  which  became  the  St.  Peter's  Sand- 
stone. And  the  ocean's  work  continued  till  the  Trenton 
Limestone  was  laid  down.  Then  dry  land  was  there  again, 
and  other  erosions  began.  The  land  surface  seems  to  have 
continued  to  our  times — and  here  we  stand,  beings  of  a  day, 
looking  on  it  as  the  outcome  of  almost  an  eternity  of  years. 
This  is  a  little  glimpse  of  the  grand  history  of  the  world. 

There  are  many  interesting  things  about  these  Cambrian 
strata,  both  in  the  Upper  Mississippi  region  and  elsewhere, 
which  must  be  passed  over  now,  because  I  only  expect  you 
to  obtain  some  very  simple  ideas  in  this  first  course  of  study. 
But  you  must  learn  something  about  these  strata  in  the 
Cincinnati  region.  If  you  look  upon  the  little  map,  you 
will  notice  that  this  region  has  coal  measures  upon  the  east 
and  upon  the  west.  So,  according  to  our  law  of  dip,  the 
Cambrian  rocks  dip  from  the  region  of  Cincinnati  toward 
the  east  on  one  side,  and  toward  the  west  on  the  other.  You 
will  notice,  too,  that  rocks  newer  than  Cambrian  exist  on  the 
north  and  south  also.  So  the  Cincinnati  rocks  dip  north- 
ward on  the  north,  and  southward  on  the  south.  You  must 
try  to  picture  that  arrangement  to  your  mind's  eye.  When 
you  go  to  Cincinnati,  you  will  see  the  high  hills  surrounding 
the  city  on  three  sides.  From  the  tops  of  the  hills  the 
country  extends  somewhat  level  as  far  as  you  can  see. 
When  you  visit  the  hills  you  will  notice  the  out-cropping 
edges  of  limestones  and  shales  and  clay  strata.  From  these 
outcrops  these  strata  pass  into  the  hills,  under  the  country 


TO  THE   UPPER   MISSISSIPPI. 


139 


on  all  sides.  If  we  were  to  construct  a  section  across  this 
region  from  east  to  west,  it  would  look  somewhat  like  this 
diagram,  Figure  56.  The  Potsdam  Sandstone  is  underneath 


h  fedcb  a  bcdeg 

FIG.  56. — SECTION  ACROSS  THE  CINCINNATI  SWELL.  C.  Cincinnati,  a.  b. 
Cambrian,  c.  Silurian,  d.  Devonian,  e.  Waverly.  /.  Carboniferous 
Limestone,  g.  Equivalent  of  Carboniferous  Limestone  on  the  easterly 
side.  h.  Illinois  Coal  Field,  i.  Appalachian  Coal  Field. 

the  Trenton  Group,  which  is  the  only  Cambrian  here 
exposed.  We  find  nothing  here  called  St.  Peter's  Sandstone, 
but  geologists  believe  that  the  rocks  immediately  below  the 
Trenton,  before  we  come  down  to  the  Potsdam  proper, 
correspond  to  the  St.  Peter's  Sandstone  and  the  Lower 
Magnesian  Limestone. 

The  Potsdam  Sandstone  is  not  everywhere  the  formation 
which  rests  immediately  on  the  Eozoic.  In  Nova  Scotia, 
in  eastern  Massachusetts  and  northwestern  Vermont,  and 
in  many  other  regions,  are  slaty  strata  older  than  the  Pots- 
dam and  called  Acadian.  So  in  different  regions  are  other 
differences  in  the  kinds  of  rocks.  But  geologists  have 
agreed  to  arrange  all  the  Cambrian  strata,  in  all  parts  of  the 
country,  in  three  groups  ;  and  here  are  their  names  : 


CAMBRIAN  SYSTEM  * 


Trenton  Group.     Same  as  described  in  Wisconsin  and 

at  Cincinnati. 
Canadian  Group.      Includes  St., Peter's   Sandstone 

and  Lower  Magnesian  Limestone. 
Primordial  Group.     Includes  Potsdam  Sandstone  and 

Acadian  Slates. 


140  GEOLOGICAL   EXCURSIONS. 

EXERCISES. 

What  system  of  rocks  occupies  the  surface  between  Cincinnati 
and  Frankfort,  Ky.  ?  Which  way  do  these  rocks  dip  at  Frank- 
fort ?  How  far  in  that  direction  do  they  continue  under  newer 
rocks?  Where  do  they  come  to  the  surface  again?  What 
rocks  are  at  the  surface  in  central  Tennessee  ?  Which  way  do  they 
dip  ?  Under  what  rocks  do  they  disappear  in  southern  Ten- 
nessee ?  How  far  do  they  continue  their  dip  to  the  south  of 
Tennessee?  Do  the  Cambrian  strata  pass  under  Mobile  ?  What 
rocks  are  at  the  surface  at  Mobile  ?  What  system  of  rocks  must 
be  bored  through  at  Mobile  before  reaching  the  Potsdam  for- 
mation ?  Put  yourself  at  the  city  of  Green  Bay,  Wis.,  and  walk 
along  the  outcropping  edge  of  the  formation  ;  in  what  direction 
do  you  travel  ?  Which  side  of  Green  Bay  will  you  travel  to 
keep  on  the  Cambrian  strata?  How  far  can  you  travel  along 
those  strata,  and  what  places  will  you  pass  ?  Name  some  places 
in  New  York  which  are  on  Cambrian  strata.  Mention  all 
the  Cambrian  regions  in  the  United  States. 


EXCUKSION  XXIY.— To  Niagara  Falls. 
Silurian  Hocks  and  History. 

When  we  stand  by  the  brink  of  the  world-renowned 
Falls  of  Niagara,  we  see  an  enormous  mass  of  water  pour- 
ing over  a  precipice  into  a  deep  and  fearful  gorge.  The 
sublimity  of  the  scene  absorbs  all  our  attention  and  all  our 
interest.  Still,  we  must  present  ourselves  at  Niagara  in  a 
mood  to  study  the  causes  of  this  stupendous  cataract.  It 
is  an  excellent  place  for  one  who  wishes  to  get  some  insight 
into  the  great  facts  and  teachings  of  geology. 

First,  there  is  the  great  gorge  a  hundred  and  fifty  feet 
deep  down  to  the  water;  and  then  at  least  a  hundred  and 


TO    NIAGARA    FALLS. 


141 


fifty  feet  still  deeper  beneath  the  surface  of  the  rushing 
river.  Look  along  the  walls  of  the  gorge.  There  are 
numerous  distinct  beds  or  strata  of  rock  divided  from  each 


FIG.  57.— TABLE  ROCK  AS  IT  WAS. 

other  by  joints  or  seams.  Your  eye  can  trace  them  a  long 
distance  down  the  stream  toward  the  old  railway  suspension 
bridge.  Notice  that  they  all  continue  to  rise  slowly  nearer 
the  surface  as  they  extend  northward  down  the  stream. 
Walk  down  to  the  bridge.  You  can  trace  these  strata 
all  the  way.  You  see,  however,  that  they  gradually  rise. 
You  may  take  the  railway  which  runs  along  the  bank  of  the 
gorge  on  the  American  side  to  its  termination,  about  five 
miles  below.  Here,  if  you  look  east  or  west,  you  see  a 
high  bluff  of  rocks  facing  north  toward  Lake  Ontario. 
This  great  Niagara  gorge  looks  as  if  it  had  been  worn 
out  by  the  river.  We  think  it  has. 

If  you  return  to   the   Falls,  you    see   that  the  rock  at 
the  surface  there  is  a  limestone.     The  Falls  pour  over  the 


142 


'   GEOLOGICAL   EXCURSIONS. 

235ft. 


broken  edge  of  it.     This 
is  the  Niagara  Limestone. 
You  can  trace  it  along  the 
upper  part   of  the   gorge 
all   the  way  to  Lewiston. 
Different  strata  of  it  keep 
coming  to  the  surface  and 
terminating.     It  must   be 
much    thinner,    therefore, 
at  Lewiston  than  it  is  at 
the     Falls.       Above     the 
Falls  it  may  be  traced  to 
the  head  of  the  "Kapids." 
There  is  a  way  by  which 
curious    and    adventurous 
people  may  go  behind  the 
Falls,  so  that  the  mighty 
cataract    pours    down    in 
front  of  them.     It  is  a  wet 
and  slippery  place,  but  we 
can    learn    some   geology 
there.     Above    us   is   the 
great   Niagara   Limestone 
— here  we  are,  underneath 
it.     We  see   that  it  rests 
on  a  thick  mass  of  shale. 
This  shale  is  a  part  of  the 
series  of  strata,   and  may 
be  traced  along  the  gorge 


38  ft.  above  L.  Erie 


TO    NIAGARA    FALLS.  143 

all  the  way  to  Lewiston.  It  is  the  so-called  Niagara  Shale. 
At  this  place  it  is  worn  away  from  under  the  limestone, 
and  makes  the  shelter  where  we  stand.  It  is  continually 
crumbling  down,  and  making  the  shelter  deeper.  Some- 
times it  gets  so  deep  that  the  overhanging  limestone  is  not 
strong  enough  to  bear  its  own  weight  and  the  weight  of  the 
water  over  it.  Then  great  blocks  of  the  limestone  break 
off,  and  fall  down  into  the  abyss  of  foaming  water.  Thus 
the  brink  of  the  precipice  is  moved  a  little  farther  up 
stream,  and  the  brink  of  the  Falls  is  also  moved.  This  is 
the  "recession  of  the  Falls."  Now  it  may  be  that  this 
shows  how  the  whole  gorge  has  been  made  all  the  way 
from  Lewiston.  But  the  extension  of  the  gorge  by  such 
means  would  be  slow,  you  say.  Well,  it  has  been  shown 
that  the  Falls  have  receded  one  hundred  feet  in  thirty-three 
years.  That  is  considerable. 

In  Figure  57  is  shown  a  remarkable  projecting  table  of 
the  Niagara  Limestone  on  the  Canadian  side.  This  was 
formerly  a  striking  feature  of  the  spot,  but  it  exists  no 
more.  People  used  to  enjoy  the  excitement  of  standing 
upon  it.  But  eventually  "Table  Rock"  broke  off  by  frag- 
ments, and  fell  to  the  bottom  of  the  gorge.  Goat  Island 
is  disappearing  in  a  similar  way.  So  the  work  of  erosion 
goes  on  before  our  eyes. 

Underneath  the  Niagara  Shale  may  be  traced  a  thin 
band  of  limestone,  with  a  thin  band  of  shale  under  it. 
These  represent  the  Clinton  formation,  which  in  some 
regions  is  much  more  important  than  here,  and  contains 
beds  of  iron  ore, — but  quite  different  from  that  of  the 


144  GEOLOGICAL   EXCUESIONS. 

Eozoic.  Below  these  strata,  in  the  lower  part  of  the  gorge, 
may  be  seen  strata  of  red,  gray  and  variegated  sandstone. 
This  is  the  Medina  Sandstone,  and  it  passes  downward 
into  the  Oneida  Conglomerate.  The  Medina  Sandstone  is 
quarried  near  Eochester  quite  extensively,  for  sidewalks, 
pavements  and  building  purposes.  All  these  formations 
together  make  up  the  so-called  Niagara  Group  of  rocks. 

If  you  look  on  our  little  geological  map,  you  will  trace 
the  Silurian  System  of  rocks  eastward  from  the  Niagara 
Kiver  through  central  New  York.  In  Onondaga  and  Cayuga 
counties  we  have  fine  opportunities  to  see  the  formation 
which  lies  next  above  the  Niagara  Group.  It  consists  of 
shales,  clays  and  impure  limestones,  with  abundance  of 
brine  and  considerable  beds  of  gypsum.  The  latter  is  often 
ground  into  plaster  to  spread  on  farming  lands,  or  to  burn 
till  all  the  water  is  driven  off,  and  then  employ  in  plastering 
the  walls  of  houses.  The  brine  oozes  out  of  the  formation, 
and  saturates  the  marshes  at  Syracuse.  In  these  wells  are 
dug,  and  the  brine  is  pumped  out  for  boiling  away  to  make 
salt.  This  is  the  Salina  Group.  Its  outcrops  extend  west 
from  Syracuse  to  the  Niagara  Eiver  above  the  Falls  (see 
Figure  58),  and  thence  through  Canada  to  Lake  Huron. 
You  can  trace  it  on  the  map.  Its  place  is  south  of  the 
middle  of  the  Silurian  belt  everywhere.  At  Goderich,  on 
Lake  Huron,  wells  are  bored  till  they  reach  the  Salina 
Group,  and  rock  salt  is  actually  found.  At  Alpena,  in 
Michigan,  the  same  has  been  done.  Well,  if  rock  salt  can 
be  found  in  this  formation  in  Canada  and  Michigan,  why 
not  in  New  York?  So  queried  some  New  York  gentlemen, 


TO   NIAGARA   FALLS.  145 

encouraged  by  the  geologist,  and,  by  boring  in  western 
New  York,  they  also  found  rock  salt.  And  now  the  regions 
about  Warsaw  and  Le  Roy,  in  Wyoming  and  Genesee 
counties,  are  new  centres  of  great  activity  in  salt  produc- 
tion. Why  should  they  not  bore  south  of  Syracuse  and 
find  rock  salt? 

Now,  if  we  try  to  trace  the  Niagara  and  Salina  groups 
eastward  toward  the  Hudson  River,  we  find  them  growing 
thinner,  and  becoming  lost  to  observation.  But,  on  the 
other  hand,  some  limestone  beds  above  the  Salina,  which 
are  thin  in  western  and  central  New  York,  become  much 
thicker  in  eastern  New  York,  and  form  the  basal  portion 
of  the  Helderberg  Mountains,  which  may  be  seen  to  the 
south  of  the  Central  railroad  when  traveling  a  few  miles 
west  of  Albany.  These  limestones,  together  with  some 
shales,  form  the  Helderberg  Group.  This  can  be  traced 
westward  from  Buffalo  to  the  islands  in  the  western  end 
of  Lake  Erie,  and  thence  south  through  central  Ohio, 
covering  a  broad  belt  just  off  the  western  border  of  the 
Devonian.  It  is  found  also  in  Indiana,  Illinois  and  Mis- 
souri; as  also  in  Massachusetts,  New  Hampshire  and  Maine; 
and  very  extensively  in  the  provinces  of  Quebec,  New 
Brunswick  and  Nova  Scotia.  So  the  Silurian  System  is 
made  up  of  these  groups  as  follows: 

f  Helderberg  Group. 
SILURIAN  SYSTEM  -j  Salina  Group. 
[  Niagara  Group, 


146  GEOLOGICAL   EXCURSIONS. 

EXERCISES. 

What  part  of  Ontario  has  Silurian  rocks  at  the  surface?  Of 
what  age  are  the  cliffs  along  the  east  side  of  Green  Bay?  Of 
what  age  are  those  on  the  west  side  ?  Suppose  a  deep  well  is 
bored  at  Cincinnati,  would  it  ever  reach  Silurian  rocks?  Explain 
this.  Mention  some  other  city  geologically  situated  like  Cincin- 
nati. Name  all  the  important  cities  built  on  Silurian  rocks. 
Of  what  age  is  the  limestone  quarried  near  Chicago  ?  Can  you 
name  towns  near  Chicago  which  are  famous  for  their  fine  quar- 
ries? Are  there  any  Silurian  quarries  in  Massachusetts?  The 
Manitoulin  Islands  are  Cambrian  on  one  border  and  Silurian  on 
the  other;  which  border  should  be  Silurian  ?  Which  way  do  the 
strata  dip  at  Madison,  Wis.  ?  Are  there  any  Niagara  Limestone 
quarries  in  the  Lower  Peninsula  of  Michigan  ?  Could  there  be 
any  limestone  quarries  at  Milwaukee?  If  there  are  any  limestone 
quarries  at  Rochester,  N.  Y.,  what  is  the  name  of  the  limestone  ? 
Are  there  any  limestone  quarries  at  Potsdam,  N.  Y.?  Should  an 
artesian  well  be  bored  at  Chicago,  what  is  the  first  sandstone 
formation  which  would  be  reached  ?  Where  does  that  sandstone 
come  to  the  surface?  Where  do  the  rains  go  which  fall  on  that 
sandstone  in  the  region  of  its  outcrop  ? 


EXCURSION  XXV.—  To  MacUnac. 
Devonian  Bocks. 

In  the  straits  connecting  Lake  Michigan  with  Lake 
Huron  is  a  small  island,  which  you  can  hardly  find  on  the 
map,  called  Mackinac  Island.  But  when  you  pass  that  way 
on  a  steamer,  you  see  it  rising  318  feet  above  the  water,  and 
bounded  on  all  sides  except  the  south  by  a  perpendicular 
wall  of  limestone.  This  island  is  a  delightful  place  of  sum- 
mer resort. 


TO   MACKINAC.  147 

On  the  west,  on  the  main  land  of  the  Upper  Peninsula, 
and  south,  on  the  main  land  of  the  Lower  Peninsula,  rise 
high  bluffs  of  the  same  kind  of  limestone,  though  not  so 
high.  One  cannot  help  believing  these  bluffs  were  once 
connected  with  Mackinac  Island.  Here,  in  Figure  59,  is  a 
a  section  through  the  island. 
You  see  the  same  flinty  con- 
glomerate  at  the  base  of  the 
island  and  at  the  base  of  Kab-  FlGURE  59.-sECTioN  SOUTHEAST  AND 

NORTHWEST  THROUGH  MACKINAC  ISL- 

bit's    Back    On    the    main   land.         AND.    DEVONIAN  ROCKS,    a,  Old  Fort 

Holmes;  &,  Sugar  Loaf;  c,  Robinson's 

You  also  see  the  same  broken      Foiiy,  a,  Rabbits  Back  on  the  upper 

,.  ,  ,  ,  Peninsula;   e.  Round  Island;  f,  Con- 

limestone    above    the  COngloiTl-        giomeritic  Stratum;  m,  Surface  of  the 

erate    at    both    places.      The      Lake' 

deep  valleys  between  the  island  and  the  main  land,  and 
between  the  island  and  Round  Island,  have  been  dug  out 
of  the  solid  limestone,  and  into  the  Niagara  limestone, 
which  lies  below,  by  some  agency  of  wonderful  power. 
The  valleys  are  now  occupied  by  the  water  of  the  straits. 
In  fact,  these  limestones  have  been  dug  away  through  the 
whole  width  of  the  straits,  and  only  Mackinac  Island 
remains  near  the  narrowest  part,  to  show  us  how  high  the 
rocks  were  once  piled.  This  is  another  case  of  vast  erosion, 
which  reminds  us  of  what  can  be  seen  at  Niagara  gorge. 
But  there  is  no  reason  to  think  it  was  done  by  a  river.  And 
yet,  let  us  consider  a  moment.  The  water  from  Lake  Michi- 
gan flows  through  these  straits  and  Lake  Huron.  Suppose 
the  straits  not  yet  dug  through.  Suppose  the  solid  lime- 
stone stretches  across  from  Old  Mackinac,  on  the  Lower 
Peninsula,  to  Rabbit's  Back.  Lake  Michigan  would  then 


148 


GEOLOGICAL   EXCURSIONS. 


be  dammed  up.  The  rivers  flowing  into  it  would  fill  the 
lake  till  the  water  would  be  high  enough  to  flow  over  the 
Mackinac  barrier  ;  and  then  a  river  would  exist  there.  Per- 
haps a  great  waterfall  once  existed  there,  and  dug  a  gorge 
like  Niagara,  and  the  gorge  receded  till  the  limestone  bar- 
rier was  cut  through.  Then  Lake  Michigan  was  drained  to 
the  level  of  Lake  Huron.  Now,  I  do  not  say  all  this  has 
happened,  but  you  can  understand  that  it  may  have  hap- 
pened. Such  reasoning  as  to  how  things  have  been  made 
as  they  are,  belongs  to  geological  theory.  I  do  not  intend 
to  offer  you  theories  in  connection  with  these  Excursions, 
but  you  ought  to  know  what  we  mean  by  theories. 

The  principal  mass  of  Mackinac  Island  rises  only  about 
150  feet  above  the  lake,  and  forms 
a  plain,  covered  by  a  forest  growth. 
At  one  point  rises  a  cone-shaped 
remnant  of  the  higher  limestone, 
134  feet  above  this  plain.  The 
higher  limestone  forms  a  smaller 
or  upper  plateau,  294  feet  feet 
above  the  lake.  (See  Figure  60.) 

On  one  of  the  sides  of  the  island 
the  waves  have  worn  through  the 
bounding  cliffs,  and  dug  under 

the  upper  strata  of  the  limestone,  leaving  a  real  natural 
bridge.  Both  these  works  of  geological  erosion  are  great 
natural  curiosities.  There  are  also  overhanging  cliffs  and 
caverns  which  always  interest  the  visitor.  The  Indians 
had  many  romantic  tales  connected  with  these  localities. 


FIG.  60.— VIEW  OF  "SUGAR 
LOAF,"  MACKINAC  ISLAND. 
Devonian  Limestone. 


TO    MACKI2STAC. 


149 


A  cavern  in  the  west  escarpment  is  connected  with  tradi- 
tions as  thrilling  and  probably  as  mythical  as  those  about 
the  "Dragon's  Cave"  on  the  Drachenfels. 

The  limestone  of  this  island  and 
vicinity  is  called  the  Corniferous 
Limestone,  and  it  belongs  to  the 
lower  part  of  the  Devonian  System. 
You  will  please  turn  frequently  to 
the  "Geological  Column,"  page 
99,  so  as  to  keep  track  of  the  for- 
mations about  which  you  learn. 
Now,  if  you  examine  the  Geolog- 
ical Map,  you  will  see  that  the 
Devonian  extends  westward  from 
Old  Mackinac  to  Little  Traverse 
Bay.  As  the  dip  of  the  strata  is 
southward,  you  perceive  that  Little 

Traverse  Bay  must  be  excavated  in  the  higher  strata  of  the 
Devonian  System.  In  fact,  when  we  get  to  the  head  of 
Little  Traverse  Bay,  we  find  a  cliff  of  a  different  kind  of 
limestone  ;  and.  as  we  follow  around  the  coast  toward 
Grand  Traverse  Bay,  we  see  still  other  strata  coming  in 
higher  up  the  series.  They  consist  of  limestones,  shales 
and  clays,  and  are  packed  full  of  fossil  shells  and  corals. 
The  highest  formation  in  this  series  is  a  black  shale  charged 
with  carbonaceous  and  bituminous  matter.  This  series  of 
strata  forms  the  "Hamilton  Group."  The  high  bluffs 
which  the  Hamilton  Limestones  form  on  Little  Traverse 
Bay  afford  sightly  and  delightful  situations  for  summer 


FIG.  61.— "ARCHED  ROCK," 
MACKINAC  ISLAND.  Devo- 
nian Limestone. 


150  GEOLOGICAL   EXCUKSIONS. 

resorts.  Here,  and  near  here,  are  Petoskey,  Bay  Yiew  and 
Charlevoix. 

A  little  farther  toward  the  centre  of  the  Peninsula  we 
find  beds  of  shales  and  clays  next  in  order  above  the  Ham- 
ilton Group.  They  attain  a  thickness  of  seven  or  eight 
hundred  feet,  and  constitute  the  Chemuny  Group.  They 
contain  here  very  few  fossils. 

Now,  look  again  at  the  Geological  Map,  and  trace  the 
Devonian  System  eastward.  You  see  it  passes  under  Lake 
Huron,  and  comes  to  light  again  on  the  southeast  shore. 
Goderich  stands  on  the  Corniferous  Limestone  ;  so  do  Lon- 
don, Ingersoll  and  Woodstock.  The  system  also  passes 
under  a  large  part  of  Lake  Erie.  In  New  York  you  see 
Buffalo  on  the  lower  part  of  the  system.  Near  Buffalo  are 
found  many  fine  Hamilton  fossils.  Farther  east,  we  have 
Caledonia,  Le  Roy  and  the  higher  part  of  Syracuse  on  the 
Corniferous  Limestone.  This  limestone  forms  prominent 
ridges  throughout  its  whole  extent  from  Mackinac.  You 
see  it  strike  east  and  west  through  central  New  York.  At 
Syracuse  it  rises  in  a  lofty  ridge,  which  is  cut  through  by 
Onondaga  Creek.  This  runs  north  into  Onondaga  Lake. 
On  each  side  of  the  valley  of  that  creek  are  high  lime- 
stone bluffs  which  present  much  fine  scenery.  Here  is  the 
old  settlement  of  Onondaga  Hill  on  the  west  side.  On  the 
east  is  Syracuse  University. 

Under  the  Corniferous  Limestone,  we  find  along  this  val- 
ley a  coarse,  decomposing  conglomeritic  sandstone  contain- 
ing fossils  quite  unlike  those  of  the  Corniferous.  This  is 
the  Oriskany  Sandstone.  It  is  not  a  very  important  forma- 


TO    MACKINAC.  151 

tion,  though  we  find  it  at  intervals  from  Missouri  to  the 
Gulf  of  St.  Lawrence.  I  incline  to  regard  the  Oriskany  as 
the  base  of  the  Devonian,  though  some  geologists  prefer  to 
consider  it  the  top  of  the  Silurian. 

The  dip  of  the  strata  in  central  New  York,  as  you  will 
observe,  is  toward  the  south.  Hence,  as  you  travel  south 
toward  Cortland,  you  find  the  Hamilton  limestones  and 
shales  coining  in  above  the  Corniferous,  and,  in  fact,  piling 
up  the  strata  to  a  still  higher  level.  These  shales  are  full 
of  fossil  shells,  very  well  preserved.  If  we  go  on  from 
Cortland  still  farther  south,  we  find  the  same  kinds  of 
strata  occurring  above  the  Hamilton  as  have  been  mentioned 
in  Michigan  —  only  they  are  more  sandy  and  harder,  and 
attain  a  greater  thickness.  These  Chemung  strata  stretch 
east  and  west  through  all  the  southern  counties  of  New 
York.  They  give  rise  to  much  picturesque  scenery,  fine 
examples  of  which  may  be  seen  at  Panama,  in  Chautauqua 
county,  and  again  at  Ithaca,  and  in  the  vicinity  of  Cornell 
University.  At  Watkins'  Glen,  at  the  south  end  of  Seneca 
Lake,  the  magnificent  gorge  before  mentioned  (Figure  21) 
occurs  in  this  formation. 

Another  glance  at  the  Geological  Map  will  show  that 
much  of  the  central  part  of  Ohio  is  also  on  the  Devonian 
System  of  strata.  The  cities  of  Columbus  and  Delaware 
stand  on  the  Corniferous  Limestone.  The  Chemung  shales 
stretch  all  the  way  from  southern  New  York,  along  the 
south  shore  of  Lake  Erie,  nearly  to  Sandusky,  and  thence 
bend  southward  across  Ohio  to  the  Ohio  River.  Their  posi- 
tion on  the  map  is  along  the  east  side  of  the  Devonian  belt. 


152  GEOLOGICAL   EXCURSIONS. 

Through   Indiana,  their  place  is   on  the  west  side   of  the 
Devonian  belt. 

So  we  have  four  groups  of  rocks  to  make  up  the  Devon- 
ian System,  and  they  are  as  follows: 

fChemung  Group. 

DEVONIAN  SYSTEM  ^amilton  Group. 

Cormferous  Group. 
,         1^  Oriskany  Sandstone. 

EXERCISES. 

Now  explain  why  the  Chemung  should  be  along  the  western 
border  of  the  Devonian  in  Indiana,  but  along  the  eastern  border 
of  it  in  Ohio.  An  artesian  well  was  bored  at  Columbus,  Ohio; 
please  state  what  groups  of  strata  must  have  been  passed  through. 
Is  there  any  water-bearing  formation  underneath  Columbus  ? 
Does  it  outcrop  in  any  of  the  surrounding  states  ?  What  is  the 
nearest  outcrop  of  the  Potsdam  Sandstone  ?  What  do  you  judge 
would  be  the  prospect  of  getting  water  in  an  artesian  boring  at 
Columbus  ?  Would  the  prospect  be  any  better  at  Chicago  ? 
What  is  the  age  of  the  limestone  at  the  Falls  of  the  Ohio,  at 
Louisville  ?  What  would  be  the  first  limestone  struck  in  sinking 
a  shaft  at  Detroit?  Would  there  be  any  prospect  of  striking 
rock  salt  by  boring  at  Rochester,  New  York  ?  Which  way  do 
the  strata  dip  at  Lexington,  Kentucky?  Why  are  there  no 
Cambrian,  Silurian  or  Devonian  strata  over  the  Adirondack 
region  ?  Do  you  think  any  Silurian  rocks  ever  covered  the  site 
of  Cincinnati  ?  What  reason  can  you  give  for  thinking  as  you  do  ? 


TO    BURLINGTON,   IOWA. 


153 


EXCUKSIOJST   XXVI.—  To  Burlington,  Iowa. 
The  Lower  Carboniferous  Rocks, 

We  wish  now  to  extend  our  survey  of  the  rocks  of  our 
country  to  the  formations  above  the  Devonian.  Perhaps 
the  most  favorable  region  for  studying  the  Lower  Car- 
boniferous is  the  valley  of  the  Mississippi  Kiver  from 
near  Davenport  nearly  to  Cairo. 
Let  us  stop  at  Burlington. 
Here  we  find  a  bluff  175  feet 
high.  All  the  upper  part  —  be- 
neath 25  feet  of  loose  materials 
— is  of  limestone.  The  lower 
portion,  however,  is  composed 
chiefly  of  beds  of  yellowish  sand- 
stone. These  at  the  bottom  are 
quite  shaly,  and  are  knowrn  to 
extend  65  feet  beneath  "the  surface 
of  the  river.  A  study  of  the  fos- 
sils in  the  two  beds  of  limestone, 
7  and  8,  Figure  62,  shows  some 
fossils  not  found  anywhere  else, 
and  teaches  us  that  those  lime- 
stones ought  to  be  reckoned  as  a 
formation  quite  distinct  from  the 
sandstones  below.  The  upper 
formations,  made  of  limestones  7 
and  8,  we  call  the  Carboniferous 

T  .  ^  T  ,  to  8,  Carboniferous  Limestone.    9, 

Limestone  Group.  It  amounts  here     Drift.  R,  Mean  Height  of  River. 


FIG.  62.  —  SECTION  OF  THE 
BLUFF  AT  BURLINGTON, 
IOWA.  LOWER  CARBONIF- 
EROUS ROCKS.  (C.  A.White.) 

1  to  6,  "Yellow  Sandstones."    7 


154  GEOLOGICAL   EXCURSIONS. 

to  seventy  feet.  The  lower  formation,  made  of  the  yel- 
low sandstones,  we  designate  the  ' '  Waverly  Group. "  The 
limestone  is  full  of  the  fragments  of  "  stone  lilies."  Some 
beds,  from  two  to  four  feet  thick,  are  almost  completely 
formed  of  the  little  round  disc-like  segments  of  the  stems 
of  those  creatures.  Many  very  beautiful  and  perfect 
specimens  have  been  collected  here;  and  this  has  been  a 
favorite  collecting  ground  for  geologists  for  a  good  many 
years.  "We  note  some  layers  of  limestone  below  these  and 
above  the  sandstones  which  are  oolitic  —  that  is,  they  abound 
in  little  round  white  globules  about  the  size  of  homoeopathic 
pills.  But  oolitic  limestones  are  found  also  in  formations 
both  older  and  younger.  They,  therefore,  do  not  indicate 
any  particular  u  group  "  of  rocks.  If  we  inspect  the  sand- 
'stones,  we  see  that  they  are  fine  and  rather  soft  and  fri- 
able ;  but  as  to  their  fossils,  there  are  no  stone  lilies. 
Instead  of  them  we  find  a  great  abundance  of  bivalve 
shells.  The  oolitic  limestone  layers  are  like  them  in  this 
particular,  and  hence  belong*  in  the  same  group. 

This  great  difference  in  the  fossils  of  two  formations 
shows  one  means  by  which  we  are  able  to  distinguish  for- 
mations. We  know,  of  course,  without  regard  to  the  fos- 
sils, that  the  sandstones  are  older  than  the  limestones, 
because  they  underlie  the  limestones.  Also,  if  the  upper 
surface  of  the  sandstones  were  eroded  and  irregular,  we 
should  know  that  some  important  changes  took  place  after 
the  deposition  of  the  sandstones,  before  the  deposition  of 
the  limestones.  This  is  what  we  see  dividing  the  Eozoic 
from  the  Cambrian  rocks  in  the  section  shown  in  Figures 


TO   BURLINGTON,    IOWA.  155 

54,  55,  and  49.  The  same  is  seen  at  the  top  of  the  Lower 
Magnesian  Limestone  in  Figure  54.  Still  further,  if  the 
lower  strata  should  show  a  steeper  dip  than  the  upper,  that 
would  prove  that  the  lower,  after  their  formation,  were 
tilted  before  the  upper  were  laid  down.  In  the  same 
Figure  54.  you  see  that  the  dip  of  the  Cambrian  strata  is 
not  conformable  with  the  dip  and  crumpling  of  the  Eozoic. 
Unconformability  is  shown  also  in  Figure  50,  between  the 
systems  L  and  H,  and  between  the  systems  C  and  S.  But 
when  strata  like  those  at  Burlington  are  entirely  conform- 
able, witliout  any  intervening  erosions,  then  there  is  no 
way  to  ascertain  whether  they  were  formed  in  periods  quite 
distinct  or  not,  except  by  comparing  the  fossils  in  the  two. 
Yery  often  such  comparison  shows  two  formations  distinct 
when  they  are  not  only  conformable  and  not  separated  by 
erosion,  but  also,  are  both  of  the  same  kind  of  rock.  This, 
for  instance,  is  the  only  means  of  separating  the  Hamilton 
limestones  in  Ohio  and  Michigan  from  the  Corniferous 
Limestone  immediately  below.  Even  at  Burlington,  the 
oolitic  limestones  belong  in  the  lower  group  and  not  in  the 
upper. 

By  examining  the  Map  you  will  notice  that  the  Lower 
Carboniferous  covers  a  large  area  west  of  the  Mississippi 
Kiver.  From  northwestern  Indiana,  also,  a  belt  passes 
south  to  the  Ohio  River.  Most  of  this  is  Carboniferous 
Limestone.  At  Crawfordsville,  in  Indiana,  is  another 
locality  wonderfully  rich  in  stone  lilies.  A  large  part  of 
central  Kentucky  is  underlaid  by  this  limestone.  The 
celebrated  Mammoth  Cave  is  formed  in  it.  This  cave  was 


156  GEOLOGICAL   EXCURSIONS. 

once  merely  a  fissure  in  the  limestone.  "Water  circulated 
through  the  fissure,  and  by  degrees  made  it  larger.  This 
was  done  partly  by  wearing  the  rock,  but  chiefly  by  dis- 
solving it.  So,  in  the  course  of  time,  the  fissure  grew  to 
a  cavern  several  miles  long,  with  dozens  of  branches  and 
tortuous  passages,  and  ceilings  in  some  places  a  hundred 
feet  high,  and  glistening  by  torch-light  with  thousands  of 
crystals.  This  formation  abounds  in  caves  in  southern 
Kentucky.  Wyandotte  cave,  in  southern  Indiana,  is  also 
in  it. 

You  must  have  heard  of  the  "knobs"  and  the  uknob 
regions  "  of  Kentucky  and  Tennessee.  These  are  regions 
underlaid  by  the  Carboniferous  Limestone.  But  the  same 
fissured  condition  of  the  rock  which  has  led  to  its  wasting 
away  in  caverns  underground  has  here  led  to  similar,  but 
greater,  wasting  above  ground  ;  and  so  the  whole  surface 
is  gashed  and  gullied  in  every  direction  by  running  waters 
—  some  permanent,  and  some  merely  storm  waters  —  and 
the  portions  un wasted  by  the  gullies  stand  out  as  rock- 
covered  knobs.  The  unequal  wasting  is  due  partly  to  much 
silica  in  portions  of  the  limestone. 

If  we  follow  these  Lower  Carboniferous  Limestones  from 
northern  Alabama  along  the  east  side  of  the  Devonian 
toward  northwestern  and  northern  Pennsylvania,,  we  find 
the  limestone  giving  out.  In  place  of  limestone  are  soft 
red  shales  with  some  sandstones.  So  the  upper  group  of 
the  Lower  Carboniferous  begins  to  look  somewhat  like  the 
lower,  or  Waverly  Group  in  the  Mississippi  Yalley. 

In  Michigan  you  see  the  Lower  Carboniferous  forming 


TO   BURLINGTON,   IOWA.  157 

a  circular  belt  around  the  border  of  the  Lower  Peninsula. 
What  answers  to  the  Carboniferous  Limestone  is,  of  course, 
the  inner  portion  of  this  belt.  But  the  limestone  proper 
is  only  70  feet  thick.  It  appears  that  the  lower  portion 
of  this  group  consists  of  quite  a  different  sort  of  rocks. 
They  are  shales,  clays  and  gypsum,  with  a  great  amount 
of  brine.  This  brine  and  gypsum  deposit  is  not  found  in 
any  other  state.  But  it  is  found  in  New  Brunswick  and 
Nova  Scotia.  Now  how  do  we  know  this  Michigan  Salt 
Group  is  really  a  part  of  the  Carboniferous  Limestone 
Group  ?  Simply  because  we  find  in  it  the  same  species 
of  fossils.  The  gypsum  is  extensively  worked  near  Grand 
Eapids,  and  also,  on  the  opposite  side  of  the  state,  at  Ala- 
baster, on  the  north  side  of  Saginaw  Bay.  The  brine 
settles  down  into  the  sandstones  of  the  Waverly  Group 
and  saturates  them.  Most  of  the  salt  wells  of  the  Saginaw 
valley  are  supplied  by  borings  which  extend  down  into 
that  sandstone. 

I  suppose  you  have  seen  the  beautiful  blue  and  gray 
freestones  used  for  building  purposes  in  Cleveland,  Toledo, 
Detroit  and  other  cities  of  the  West.  A  freestone  is  simply 
a  sandstone  which  is  soft  enough  to  be  easily  worked  by 
the  stone  cutter.  This  beautiful  stone  is  the  uWaverly 
sandstone,"  and  gets  its  name  from  Waverly,  in  southern 
Ohio.  The  best  Ohio  quarries,  however,  are  at  Berea,  and 
near  Cleveland.  The  same  stone,  and  equally  valuable,  is 
quarried  also  in  Michigan,  in  Huron  county,  on  the  shore 
between  Saginaw  Bay  and  Lake  Huron.  The  place  is 
called  Grindstone  City,  because  the  world-famous  "Huron 


158  GEOLOGICAL   EXCURSIONS. 

grindstones"  are  made  there.  Similar  grindstones  are 
made  at  Berea.  Now  this  fine  stone  is  only  an  eastward 
continuation  of  the  yellow  sandstones  which  we  saw  at 
Burlington.  They  are,  indeed,  yellow  and  red  in  southern 
Michigan,  especially  in  Hillsdale  county.  Without  doubt 
some  of  the  olive  sandstones  of  northwestern  Pennsylvania 
belong  to  this  group,  if  even  some  similar  sandstones  in 
southwestern  New  York  are  not  the  same. 

In  eastern  Pennsylvania  the  Waverly  strata  have  be- 
come coarse,  grayish  conglomerates  and  sandstones,  with 
red  sandstones  beneath.  The  red  sandstones  are  generally 
thought  to  belong  in  the  Devonian,  and  to  constitute  a 
different  group,  called  the  Catskill  Group;  but  I  feel  doubt- 
ful about  the  correctness  of  this  opinion.  If  the  Catskill 
and  Waverly  belong  to  the  same  group,  then  the  name 
which  we  must  apply  to  it  is  Catskill,  for  that  name  was 
first  proposed.  These  red  Catskill  sandstones  extend 
northward,  and  form  a  large  part  of  the  Catskill  Moun- 
tains. 

In  some  parts  of  Pennsylvania  and  Virginia  the  lower 
group  contains  beds  of  coal,  forming  what  is  sometimes 
called  False  Coal  Measures.  In  eastern  Kentucky  and 
Tennessee,  at  the  top  of  the  Lower  Carboniferous,  are 
found  thick  beds  of  shale  containing  valuable  deposits  of 
coal ;  and  these  are  also  sometimes  called  False  Coal 
Measures.  They  are  also  called  subconglomerate  measures. 

So  we  have  in  the   Lower  Carboniferous   System   two 

groups  of  strata: 

( Carboniferous  Limestone  Group. 
LOWER  CARBONIFEROUS  SYSTEM  j  Waverly  Group> 


TO   BURLINGTON,  IOWA.  159 

EXERCISES. 

Mention  places  in  Illinois  which  are  on  the  Lower  Carbonifer- 
ous. Mention  places  in  the  knob  region  of  Kentucky.  Which 
way  is  the  dip  of  the  Carboniferous  Limestone  at  St.  Louis? 
Which  way  at  Grand  Rapids,  Michigan  ?  Which  way  on  Sagi- 
naw  Bay?  Does  the  Carboniferous  Limestone  pass  under  Cin- 
cinnati? Which  is  next  the  Devonian  in  Ohio,  the  Waverly 
Group  or  the  Carboniferous  Limestone  Group?  Which  way 
does  the  Lower  Carboniferous  dip  in  Indiana  ?  Which  way  does 
it  dip  in  northern  Pennsylvania  ?  Is  there  any  Lower  Carbonif- 
erous in  New  York?  If  so,  would  you  expect  it  to  be  a  limestone 
or  a  sandstone  ?  If  you  start  from  Louisville  to  sail  down  the 
Ohio  River,  do  you  approach  newer  or  older  rocks  ?  If  you  start 
from  Wheeling  down  the  Ohio,  do  you  reach  older  or  newer 
rocks  ?  Why  is  this  difference  on  the  upper  and  lower  portions 
of  the  Ohio?  Where  is  the  dividing  line?  What  are  the  newest 
rocks  found  in  the  province  of  Ontario  ?  What  formations  does 
Lake  Michigan  overlie?  Does  the  axis  of  the  lake  cross  the 
boundaries  of  the  formations  or  run  parallel  with  them  ?  Point 
out  other  lakes  or  bays  which  also  conform  in  trend  to  the  strikes 
of  the  formations  under  them  and  around  them.  Point  out  some 
lakes  or  bays  which  trend  across  the  boundaries  of  the  forma- 
tions. How  is  it  with  the  long  lakes  in  central  New  York?  If 
a  deep  artesian  well  is  bored  at  Grand  Haven,  what  formation 
will  be  passed  through  ?  Would  the  Potsdam  Sandstone  be 
reached  ?  Would  fresh  water  rise  to  the  surface  ? 


160 


GEOLOGICAL   EXCURSIONS. 


EXCURSION"  XXYII.— To  the  Coal  Mines. 
The  Coal  Measures. 

It  is  immaterial  what  great  coal-mining  region  we  visit. 
We  may  go  to  Wilkesbarre,  Pennsylvania,  to  Brazil,  Indi- 
ana, to  La  Salle  or  Jonesboro,  Illinois,  or  to  any  of  the  coal 
regions  in  Kansas,  Missouri,  Ohio,  Kentucky,  Tennessee  or 
Alabama.  We  shall  see  huge  piles  of  black  shale  rubbish 
lying  around,  and  great  heaps  of  coal  ready  for  shipment, 
and  great  numbers  of  small  cars  running  on  tramways 
which  lead  through  dark  yawning  openings  into  the  recesses 
of  the  earth.  We  shall  see  men  and  mules  going  under- 
ground for  long  distances,  and  if  we  follow  them,  we  shall 
find  extensive  passage  ways  excavated,  like  the  streets  of  a 
city,  sometimes  aggregating  several  miles  in  length.  The 
plan  in  mining  is  to  get  upon  a  coal  bed,  and  then  work 
it  out  in  all  directions.  Sometimes  the  coal  is  found  out- 
cropping on  a  hillside,  as  in  Figure  63,  and  then  it  is  only 


FIG.  63. — DRIFTING  IN  ON  A  COAL  BED.     a,  Mouth  of  the  Drift. 

necessary  to  "drift"  in.  There  is  generally  water  under 
ground,  and  hence  the  drift  should  enter  at  a  place  where  a 
slight  ascent  will  be  necessary  in  following  the  bed.  The 


TO   THE   COAL   MIKES. 


161 


water  then  flows  toward  the  entrance  to  the  mine,  and 
escapes.  Sometimes  mines  are  opened  in  places  where  the 
coal  beds  are  far  beneath  the  surface.  Then  a  "shaft"  is 
sunk,  as  is  shown  in  Figure  64  at  S,  and  when  a  coal  bed, 


Surface 


FIG.  64.— GENERAL  SECTION  IN  THE  UPPER  COAL  REGIONS  OF  PENNSYLVANIA. 

W,  Waynesburg  Seam.    P,  Pittsburgh  Seam.    S,  a  Mining  Shaft,    a  a,  Down  Cast. 

6,  Up  Cast.    w,  Sump. 

W,  is  reached,  excavations  are  made  on  both  sides.  Often 
the  same  shaft  is  sunk  to  a  second  coal  bed,  P,  and  occa- 
sionally even  to  a  third  one.  The  passages  or  gangways 
are  generally  extended  in  straight  lines  as  far  as  the  coal 
continues  satisfactory,  and  other  passages  are  opened  at 
right  angles  with  these.  On  each  side  of  these  gangways 
large  rooms  are  excavated,  but  with  walls  of  coal  left  stand- 


162 


GEOLOGICAL   EXCURSIONS. 


ing  between  them  for  the  support  of  the  roof.  In  the  course 
of  time  all  the  coal  is  mined  out,  except  large  columns  and 
walls  left  for  support.  In  some  mines  these  are  also  finally 
removed. 


Illbt 


B    A 

FIG.  65. — PLAN  OF  THE  MINES  OF  THE  BLOSSBURG  COAL  COMPANY  AT  ARNOT, 
PA.  Scale,  400  ft.  to  the  inch.  A,  the  Main  Gangway.  B,  the  Return 
Air  Course  and  Ventilating  Shaft.  The  light  portions  represent  the 
ground  worked  over  to  1872.  (After  Macfarlane.) 


TO   THE   COAL   MIKES.  163 

In  Figure  65  is  presented  a  plan  of  the  workings  in  the 
Blossburg  mines  of  Pennsylvania  in  1872.  This  is  a  por- 
tion of  a  coal  bed,  about  1,500  feet  broad  and  1,900  feet 
long,  showing  where  the  gangways  have  been  dug  out  for 
travel  and  for  ventilation,  and  also  the  rooms  or  u breasts" 
from  which  the  coal  has  been  taken.  It  shows  also  the 
large  amount  of  coal  left  for  supporting  the  roof.  These 
supports  will  ultimately  be  taken  out  also.  In  some  regions 
the  roof  rock  is  so  fragile  that  the  gangways  have  to  be 
timbered.  Even  then,  the  enormous  weight  sometimes 
crushes  the  supports,  and  occasional  disasters  happen  in 
this  way.  The  same  plan  of  mining  is  pursued,  whether 
the  mine  is  approached  by  an  adit,  as  shown  in  Figure  63, 
or  by  a  shaft,  as  shown  in  Figure  64. 

The  strata  which  make  up  the  so-called  Coal  Measures 
consist  largely  of  shales  and  sandstones.  Besides  these  we 
find  beds  of  clay,  and  generally  some  limestones.  All  this 
is  shown  in  Figure  64.  Sometimes  the  whole  thickness  of 
the  Coal  Measures  is  only  one  or  two  hundred  feet;  and 
then  we  find  but  one  or  two  beds  of  coal  thick  enough  to 
pay  for  mining.  In  other  regions  the  Coal  Measures  are 
several  hundred  feet  in  thickness,  and  then  they  contain, 
probably,  three  or  four  workable  beds.  Besides  the  work- 
able beds,  there  are  many  too  thin  to  pay  for  working. 
When  we  take  a  piece  of  the  coal  shales  and  split  it  open, 
we  are  apt  to  find  the  surfaces  beautifully  marked  by  the 
impressions  of  ferns.  All  the  delicate  outlines  and  vein- 
ings  are  as  perfect  as  if  pressed  in  a  modern  herbarium. 
In  Figure  66  are  shown  some  fern  remains  from  Illinois. 


164 


GEOLOGICAL  EXCURSIONS. 


Sometimes  we  find  fern  impressions  on  the  coal  itself.  In 
the  shales  we  find  also  the  flattened  stems  of  the  trees  which 
bore  the  fern  fronds  arid  other  foliage.  Sometimes,  in  the 


FIG.  66.— IMPRESSIONS  OF  FERNS  ON  COAL  SHALE.    Alethopteris  Mazoniana, 

Lesquereux. 
a,  Enlarged  Pinnules  showing  the  Nervation. 

sandstones,  the  tree  trunks  remain  unflattened,  and  even 
stand  vertically  in  the  midst  of  the  rock.  It  is  curious  to 
think  that  these  tree  trunks  may  exist  several  hundred  feet 
under  ground.  There  they  stand  where  they  grew,  and  the 
sand  has  been  accumulated  around  them.  Figure  67  gives 
a  view  of  one  of  these  trees  restored  —  that  is,  completed  as 
we  think  it  originally  appeared.  By  the  side  are  some  por- 
tions represented  on  a  larger  scale.  Figure  68  is  a  restora- 


TO   THE   COAL   MINES. 


165 


tion  of  another  sort  of  tree  whose  remains  are  very  abundant 
in  the  Coal  Measures. 

In  the  western  states  the  strata  of  the  Coal  Measures  are 


FIG.  67.  —  LEPIDODENDRON.  A  TREE 
OF  COAL  MEASURE  TIMES.  SEPA- 
RATE PARTS  ON  A  LARGER  SCALE. 
(Zittel.) 


FIG.  68. — SIGILLARIA.  A  TREE  OF 
COAL  MEASURE  TIMES.  SEPA- 
RATE PARTS  ON  A  LARGER 
SCALE.  (Zittel.) 


pretty  evenly  laid  down.     Figure  69  presents  a  general  view 
of  the  coal-bearing  strata  of  Illinois.      You  see  the  shales, 


FIG.  69. — SECTION  IN  THE  COAL  MEASURES  OF  ILLINOIS. 


166 


GEOLOGICAL   EXCURSIONS. 


sandstones  and  coal  beds  are  flat  and  nearly  horizontal,  and 
parallel  with  each  other.  But  now  look  at  this  section 
through  the  Coal  Measures  of  Pennsylvania,  shown  in 
Figure  TO.  The  different  strata  are  nearly  parallel  with  each 


FIG.  70.— SECTION  IN  THE  APPALACHIANS  Six  MILES  IN  LENGTH,  SHOWING 
PLICATIONS  OF  THE  COAL  MEASURES  AND  OLDER  STRATA.     (Rogers.) 

other,  but  notice  how  they  are  all  bent  and  broken.  This 
is  also  remarkably  shown  in  Figure  26.  Sometimes  at  the 
place  where  a  break  occurs,  we  find  the  strata  let  down  on 
one  side  below  the  level  of  the  stratum  on  the  other  side 
of  the  break.  This  is  called  a  Fault.  The  downthrow 
may  be  any  distance.  In  some  cases  it  amounts  to  twenty 
thousand  feet,  and  even  more.  Faults  occur  in  all  forma- 
tions—  especially  those  as  old  as  the  Coal  or  older.  Here, 
in  Figure  71,  is  a  series  of  remarkable  faultings  in  the 


Faults  Jrvm  600  to  1, 700 feet 


WASATCH  PLATEAU 
11, 000 ft.  high 


W 


c  b          c          c          b 

FIG.  71. — SECTION  EAST  AND  WEST  IN  CENTRAL  UTAH,  SHOWING  NUMEROUS 

FAULTS.     (Button.) 
a,  Triassic.    ft,  Jurassic,    c,  Cretaceous,    d,  Laramie.    0,  /,  Tertiary. 

Mesozoic  and  Caenozoic  strata  of  central  Utah.  You  will 
understand  that  a  fault  results  from  an  enormous  break 
through  the  whole  thickness  of  the  solid  rocks.  What  an 


TO   THE   COAL   MINES.  167 

enormous  power  is  required  to  break  a  pile  of  strata  a  mile 
or  more  thick ! 

The  lowest  stratum  of  the  proper  Coal  Measures  is 
almost  everywhere  a  conglomerate  or  pebbly  sandstone, 
called  the  Millstone  Grit.  It  is  often  so  thick  as  to  consist 
of  several  strata.  It  contains  a  good  many  remains  of 
sticks,  roots  and  foliage.  Beneath  this  there  are  generally 
some  shales,  and  in  Kentucky  and  Tennessee  excellent  beds 
of  coal.  The  Coal  Measures,  when  traced  westward,  are 
found  to  contain  less  coal  and  more  limestone.  But  higher 
up,  we  find  in  our  western  territories,  as  well  as  in  Europe, 
some  strata  which  much  resemble  the  Coal  Measures.  But 
the  fossil  remains  are  diiferent,  and  these  strata  are  set 
clown  as  forming  the  Permian  Group. 

So  the  Upper  Carboniferous  System  is  composed  of  two 
groups : 

{     Permian  Group. 
UPPER  CARBONIFEROUS  SYSTEM    \     _,    .  ,r 

|     Coal  Measures. 

EXERCISES. 

Have  you  ever  seen  a  coal  mine?  If  so,  what  did  you 
consider  the  most  interesting  thing  about  it  ?  If  not,  what 
would  you  expect  to  be  most  interested  in?  Where  does  the 
water  come  from  which  we  generally  find  in  coal  mines  ?  In 
what  part  of  the  country  are  the  strata  of  the  Coal  Measures 
most  folded  and  disturbed?  How  would  the  coal  beds  lie  in 
Michigan  ?  Are  there  any  coal  beds  in  any  New  England  state  ? 
Do  you  notice  any  connection  between  a  disturbed  condition  of 
the  strata  and  a  mountainous  condition  of  the  surface  ?  Name 
the  states  east  of  the  Mississippi  through  which  the  mountains 
extend.  Would  you  expect  the  coal  strata  to  be  folded  in  all 
those  states?  Would  they  be  equally  folded  in  western  Penn- 


168  GEOLOGICAL   EXCURSIONS. 

sylvania  ?  Is  there  any  mineral  coal  in  New  York  ?  If  you 
should  see  any  person  digging  for  coal  in  that  state,  what  would 
you  think  of  his  knowledge  of  geology?  Name  any  other 
states  which  contain  no  coal.  What  was  the  coal  formed  from  ? 
Did  those  coal  plants  grow  on  land  or  in  the  water  ?  Where  was 
the  land  when  they  were  growing  ?  Was  the  Millstone  Grit 
formed  on  the  land  ?  Can  you  think  how  tree  trunks  came  to 
stand  erect  in  the  midst  of  sandstone?  Where  might  New 
Orleans  send  to  get  coal  by  water?  Which  must  send  farthest 
for  coal,  New  Orleans  or  Mobile  ?  Are  there  any  building  stones 
in  Alabama? 


EXCUKSION  XXVIII.— To  Selma,  Alabama. 
The  Mesozoic  Rocks. 

If  you  cast  your  eyes  once  more  on  our  little  geological 
map  you  will  notice  the  city  of  Selma  located  on  the  Ala- 
bama Kiver  in  the  midst  of  a  broad  belt  of  Cretaceous  rocks 
stretching  east  and  west  across  the  state  of  Alabama.  A 
little  to  the  north  are  Silurian  and  Cambrian  rocks,  and,  to 
the  south  of  this  belt,  the  Tertiary  strata  stretch  to  the 
Gulf  of  Mexico.  At  Selma  the  Alabama  River  has  exca- 
vated a  deep  channel  through  a  whitish  chalky  limestone 
known  as  the  "  rotten  limestone."  The  city  stands  eighty 
feet  above  the  river  at  low  water.  It  is  supplied  with  fresh 
water  by  a  large  number  of  artesian  wells. 

The  "rotten  limestone"  is  near  the  upper  part  of  the 
Cretaceous  System,  and  is  about  300  feet  thick.  It  dips 
southward  beneath  the  Tertiary  rocks.  Under  this  lime- 
stone is  a  vast  series  of  sandstones,  sands  and  shales.  These 
outcrop  at  various  distances  to  the  north  of  Selrna — all 


TO   SELMA,  ALABAMA. 


169 


dipping  southward  under    ^| 
the    "rotten    limestone." 
Farther  west,  this  belt  of    &  5  ^ 

O 

Cretaceous    rocks     bends    1 1  ^ 

•=  §"'  £* 
northward,   and   the   dips    g  ^  'j 

are  first  southwest,  and  g  <;  | 
farther  north  they  are  •  |- 1 

^  o 

west.  You  see  this  Cre-  gl| 
taceous  belt  extends  even  §•  5  ^ 
to  the  mouth  of  the  Ohio  f  1  | 

on    p     >> 

River.     In  Alabama,  the  §  ?  | 

lower    strata    outcrop    at  '^  |  * 

higher     levels    than    the  1 3  ° 

upper   strata.     The   rains  •§  q  § 

which  fall  on  these  lower  |  |  « 

p    o    .3 

sandy   strata    are    carried    |  ^  w 

down    under    Selma    and    g.  M  g 

M  52 
all  other  localities  on  the    J_  |  c 

"rotten   limestone."      So    Sjq 
when     a    well    is    bored    ||  | 
at    these    localities    deep 
enough  to  reacli  the  deep 
water-bearing    strata,    the     I  | ,$  * 
water  rises  to  the  surface. 
Now  here  is  a  section 
naming   south  from  Tus- 
caloosa    to    St.    Stephens 
on   the   Tombigbee  River 
and     thence    to     Mobile. 


|M^ 


Iff)  Coal'Mines 
i  TUSCALOOSA 


Foster's  Ferry 


Carthage 

I  Havana 
Bridgeville 


/ 


k  Clinton 
EUTAW 
'Finch's  Ferry 


Hamburg 


ICHOCT AW  BLUFF 

A'eivbern 

SELMA 

J  Pleasant  Ridge 
*  Bogue  Cliillo  Creek 

PRAIRIE    BLUFF 

'  Camden 

'Black's  Bluff 
'  Bell's  Landing 


CLAIBORNE 

'stave  Creek 
iSuggsville 
1  Jackson 


!  MOBILE 
Mobile  Bay 


170  GEOLOGICAL   EXCURSIONS. 

Numerous  localities  are  named  on  it,  but  many  of  them  do 
not  concern  us  at  present.  You  see  plainly  how  all  the 
strata  dip  southward.  Here  are  several  artesian  wells  indi- 
cated. Among  them  are  two  at  Selrna.  Notice  how  they 
extend  into  the  lower  Cretaceous  formations,  which  contain 
sandy  strata.  Here  then,  you  have  a  good  explanation  of 
artesian  wells.  Notice  the  elevation  of  Eutaw.  It  is 
higher  than  the  place  of  outcrop  of  any  of  the  underlying 
Cretaceous  rocks ;  therefore  the  water  does  not  rise  to  the 
surface,  though  the  well  is  very  deep.  There  are  hundreds 
of  artesian  wells  bored  through  the  rotten  limestone  in  Ala- 
bama and  Mississippi.  In  some  of  them  the  water  contains 
much  sulphur  gas  (^hydrogen  sulphide),  and  others  yield  salt 
water. 

Now,  if  you  glance  westward  on  the  map,  you  notice  a 
vast  area  in  Texas  underlaid  by  Cretaceous  strata.  Then, 
farther  north  is  a  still  larger  area  stretching  through  Kansas, 
Nebraska,  Iowa,  Minnesota  and  Dakota.  All  these  strata, 
like  those  in  Alabama,  are  comparatively  unconsolidated. 
There  are,  indeed,  some  very  compact  sandstones,  but  the 
rocks  are,  throughout,  very  much  more  easily  broken  or 
crushed  than  the  rocks  of  the  Palaeozoic  formations.  Many 
of  the  strata,  especially  the  limestones,  abound  in  fossil 
shells  ;  and  there  are  many  remains  of  fishes  and  reptiles. 
In  Europe,  the  Cretaceous  System  contains  the  great  Chalk 
formation.  It  is  probable  the  rotten  limestone  of  the 
Southern  States  corresponds  to  the  European  Chalk. 

The  Cretaceous  is  the  uppermost  system  of  the  Mesozoic  : 
but  you  have  seen  from  the  diagram,  Figure  72,  as  well  as 


TO    SELMA,  ALABAMA.  171 

from  the  Map,  that  in  Alabama,  no  other  Mesozoic  forma- 
tion cornes  between  the  Cretaceous  and  the  Coal  Measures, 
which  are  Palaeozoic.  Probably,  if  we  could  go  down  and 
explore  the  rocks  under  the  Cretaceous,  all  the  way  to  the 
Gulf  of  Mexico,  we  might  find  the  other  Mesozoic  Systems 
actually  existing.  In  Texas,  you  will  see  from  the  Geologi- 
cal Map,  is  a  system  called  Jura- Trias,  which  covers  a  large 
area.  These  strata  pass  under  the  Cretaceous  in  Texas  and 
Kansas.  They  consist  mostly  of  shales  and  sandstones. 
This  Jura-Trias  System  is  really  composed  of  two  systems, 
the  Jurassic  and  Triassic.  In  some  regions,  in  consequence 
of  the  absence  of  fossils,  it  is  impossible  to  locate  the 
dividing  line  between  them,  or  to  say  positively  whether  a 
formation  is  really  Jurassic  or  Triassic.  That  is  the  reason 
why  we  say  Jura-Trias.  But  in  the  far  Northwest  and 
West,  the  two  systems  are  more  readily  separated,  and  we 
find  that  the  Jurassic  contains  nearly  five  thousand  feet  of 
shales  and  sandstones,  and  one  thousand  feet  of  limestone. 
In  Montana  these  limestones  contain  many  bones  and  teeth 
of  monstrous  extinct  reptiles  ;  but  we  must  postpone  the 
study  of  these  for  a  more  advanced  course.  The  Triassic 
in  the  Far  West  contains  over  eleven  thousand  feet  of  shales 
and  sandstones — many  of  the  latter  being  very  hard  and 
quartzose — and  about  4,500  feet  of  limestone. 

In  the  valley  of  the  Connecticut  River,  is  a  red  sandstone 
formation  called  Jura-Trias,  which  is  extensively  quarried 
for  building  stones.  At  Portland,  Connecticut,  are  quarries 
from  which  stone  is  taken  to  New  York  to  be  built  into  the 
so-called  brown-stone  fronts.  On  the  slabs  of  this  sandstone 


172  GEOLOGICAL  EXCURSIONS. 

may  be  seen  many  footprints  of  ancient  reptiles.  Some  of 
these  were  three-toed,  like  birds,  and  walked  on  two  feet  like 
birds.  The  same  sandstone  extends  to  New  Haven,  and 
also  appears  on  the  west  of  the  Hudson  River  in  New  Jersey. 
In  fact,  there  are  small  patches  of  it  at  various  localities  in 
North  Carolina  and  Virginia  resting  horizontally  in  the 
depressions  in  the  old  Eozoic  rocks.  Near  Richmond  is  a 
valuable  bituminous  coal  deposit  which  we  have  to  designate 
Jura-Trias. 

Thus,  the  Mesozoic  Great  System  is  made  up  of  three 
Systems,  as  follows  (see  also  "The  Geological  Column," 
Excursion  XVIII)  : 

f  Cretaceous  System. 
MESOZOIC  GREAT  SYSTEM  «j  Jurassic  System,  >  j^^rp,^ 

'^Triassic  System,  ) 

EXERCISES. 

Do  the  Mesozoic  strata  of  the  Atlantic  and  Gulf  regions  dip 
toward  the  ocean  or  away  from  it  ?  Explain  why  this  is  so. 
Do  you  imagine  Mesozoic  strata  extend  under  the  ocean  ?  In 
Kansas,  which  way  do  the  Cretaceous  strata  dip  ?  Did  they  ever 
dip  toward  a  large  body  of  water?  In  Dakota  which  way  do 
Cretaceous  strata  dip  ?  On  the  east  side  of  the  Black  Hills, 
which  way  do  they  dip  ?  Suppose  you  bore  an  artesian  well  at 
the  "  big  bend  "  of  the  Missouri  River,  would  you  ever  strike 
Eozoic  rocks  ?  What  Palaeozoic  rocks  are  exposed  nearest  to 
that  point  ?  Are  they  higher  or  lower  than  the  surface  at  the 
"  big  bend  "  ?  Would  your  artesian  well  at  the  "  big  bend  " 
bring  water  to  the  surface  ?  Would  an  artesian  boring  succeed 
at  Charleston,  S.  C.  ?  Mention  other  places  on  the  Mesozoic 
at  which  artesian  wells  might  succeed  ?  Are  any  human  remains 
found  in  the  Cretaceous  strata  ?  Are  any  reptilian  remains  found 
in  the  Silurian  strata  ?  Where  was  the  seashore  in  Alabama 


TO   CLAIBOR1STE,  ALABAMA.  173 

when  the  Cretaceous  sediments  were  accumulating  ?  Follow  the 
shore  line  through  other  states  east  and  west.  Where  was  the 
greater  part  of  the  American  land  at  the  beginning  of  Mesozoic 
Time  ?  Do  you  think  there  were  rivers  and  lakes  on  that  land  ? 
Into  what  water  did  the  Ohio  River  then  empty  ?  Where  was 
then  the  mouth  of  the  Mississippi?  Mention  some  rivers  which 
did  not  exist  in  Mesozoic  Time 


EXCURSION  XXIX.— To  Clailorne,  Alabama. 
The  Tertiary  Formations. 

I  took  you  to  Alabama  for  a  good  view  of  Mesozoic  rocks, 
Now  we  cannot  do  better  than  remain  here  to  examine  the 
Tertiary  rocks.  These,  in  order,  come  next  above  the 
Cretaceous,  and  we  can  use  the  same  section,  Figure  T2,  as 
I  gave  you  on  the  last  Excursion. 

Claiborne,  on  the  Alabama  River,  is  one  of  the  most  in- 
teresting geological  localities  in  the  country.  The  town  is 
built  on  a  bluff  180  feet  above  the  river,  and  here  is  one  of 
those  wonderful  southern  chutes  for  sliding  cotton  down  to 
the  decks  of  steamboats.  The  upper  part  of  the  bluff  is 
nearly  perpendicular,  and  consists  of  chalky  limestone  known 
as  the  "White  Limestone."  The  middle  portion  of  the  bluff 
is  formed  of  a  loose,  rusty-colored  sand  which  crumbles  down 
and  forms  a  slope  overgrown  with  vegetation.  The  lower 
part  of  the  bluff  consists  of  bedded,  compact,  sandy  clay, 
containing  large  oyster  shells,  of  a  different  species  from  the 
modern  oyster.  The  sandy  beds  are  densely  packed  with 
fossil  shells  in  a  fine  state  of  preservation.  They  also  con- 
tain the  teeth  and  vertebrae  of  ancient  sharks.  The  white 


174  GEOLOGICAL  EXCURSIONS. 

limestone  seen  at  the  top  stretches  east  and  west  across  the 
state.  It  forms  the  high,  white  bluff  at  St.  Stephens  on  the 
Tombigbee  River.  It  contains  many  fossil  shells,  and 
occasionally  the  bones  of  a  whale-like  dweller  in  the  sea, 
which  was  long  and  slender  like  the  fabled  sea-serpent. 
Many  years  ago  a  pretty  complete  skeleton  of  this  extinct 
monster  was  dug  out  of  the  rock  in  Clarke  county.  These 
strata  all  belong  to  the  Eocene,  or  oldest  division  of  the 
Tertiary. 

You  will  notice  particularly  three  things  about  these  Terti- 
ary strata:  1.  They  are  not  hard  rocks  like  those  of  the 
Palaeozoic  formations.  They  are  not  even  hard  as  the  Cre- 
taceous strata.  2.  The  fossils  are  much  more  like  the 
remains  of  beings  which  live  in  human  times,  and  they  come 
out  of  the  strata  in  a  more  perfect  condition.  3.  The  Terti- 
ary strata  lie  next  the  seacoast. 

This  last  point  is  made  clear  when  you  understand  that 
the  Tertiary  strata  extend  west  from  Alabama  through 
Mississippi,  Louisiana  and  Texas,  and  east  through  all  the 
Gulf  and  Atlantic  states  to  New  Jersey.  Look  on  our  little 
map  again  and  see  what  an  immense  country  is  underlaid  by 
Tertiary  strata  in  the  valley  of  the  Mississippi.  Then 
toward  the  north  notice  that  half  of  New  Jersey  is  Tertiary. 
Long  Island  is  also  thought  to  be  underlaid  by  Tertiary.  It 
certainly  has  the  level  and  sandy  appearance  of  a  Tertiary 
region.  Also  the  two  islands,  Nantucket  and  Martha's 
Vineyard  are  Tertiary.  All  these  islands  are  so  covered  by 
sand  that  it  is  almost  impossible  to  examine  the  underlying 
strata.  But  the  southwest  point  of  Martha's  Vineyard  rises 


TO    CLAIBOK^E,  ALABAMA.  175 

high  above  the  water,  and  brings  plainly  to  view  the  strata 
which  form  the  body  of  the  islands.  This  promontory  is 
called  Gay  Head.  It  is  a  favorite  excursion  for  the  summer 
sojourners  on  Martha's  Yineyard  to  make  a  steamboat  trip 
to  Gay  Head.  The  strata  here  are  mostly  clay,  and  they 
are  gaily  diversified  in  color.  Some  strata  are  blue  or  white, 
others  are  red  or  yellow  or  black ;  and  all  are  crumpled  in 
fantastic  fashion,  and  worn  in  almost  vertical  cliffs  by  the 
action  of  the  sea  and  the  weather.  We  know  these  are 
Tertiary  beds  because  we  find  in  them  sharks'  teeth  and 
whales'  vertebrae,  and  a  few  sea  shells  which  elsewhere  are 
found  in  the  Miocene  Tertiary. 

Now  notice  the  great  Tertiary  expanse  shown  on  the 
western  part  of  our  map.  There  are,  indeed,  two  of  them. 
If  this  map  embraced  the  whole  region  to  the  Pacific  Ocean, 
we  should  see  several  other  Tertiary  areas.  Now,  when 
you  remember  that  the  Tertiary  strata  are  the  last  laid  down, 
and  must,  therefore,  overlie  all  the  others,  you  can  under- 
stand that  while  the  sediments  were  forming  which  have 
hardened  into  these  patches  of  Tertiary  strata,  there  must 
have  existed  seas  or  lakes  in  the  interior  of  the  continent ; 
and  you  can  understand  that  these  Tertiary  areas  are  the 
sites  of  dried  up  seas  or  lakes.  Just  so  the  Atlantic  and 
Gulf-border  Tertiary  marks  the  site  of  the  ancient  ocean, 
which  in  this  case,  has  not  dried  up,  but  shrunken  away. 
The  retreat  of  the  ocean,  however,  has  probably  been 
caused  more  by  an  uplift  of  the  land  than  by  a  diminution 
of  the  ocean's  water ;  and  so  the  interior  seas  were  partly 
drained  by  the  same  elevation  of  the  land. 


176  GEOLOGICAL   EXCURSIONS. 

When  those  interior  seas  existed,  the  land  was  populated 
by  many  species  of  quadrupeds  which,  in  the  earlier  times, 
were  very  different  from  the  quadrupeds  which  now  live. 
In  later  Tertiary  times,  other  species  lived  which  showed  a 
growing  approach  toward  our  modern  animals.  But  it  is 
not  best  to  try  to  learn  much  about  those  strange  extinct 
animals  until  you  have  advanced  farther. 

The  sediments  which  accumulated  in  the  bottoms  of  those 
seas  are  rocks  now.  They  consist  mostly  of  clays,  sands 
and  incoherent  sandstones.  They  are  made  of  stuff  washed 
in  from  the  surrounding  land.  Who  can  say  how  much  of 
the  land  was  worn  out  to  furnish  the  material  for  the  Terti- 
ary strata  ?  So,  in  every  age,  the  work  of  previous  ages  has 
wasted  away,  and  the  old  materials  have  been  rebuilt  in  the 
monuments  of  the  passing  time. 

But  it  is  long  sinfce  these  ancient  seas  were  thus  partly 
filled  and  completely  drained.  The  strata  then  new-made 
have  in  turn  become  the  broken  and  decaying  formations  of 
the  age  now  passing.  The  rains  and  the  streams  have  ever 
since  been  doing  the  same  kind  of  work  upon  these  last 
formed  strata,  as  they  did  in  the  older  time  to  get  the  stuff 
to  make  these  strata.  These  rocks  are  so  incoherent  that 
nature's  erosive  agencies  have  wrought  vast  destruction 
among  them.  In  some  regions  immense  basins  have  been 
dug  out  right  in  the  midst  of  a  Tertiary  region,  and  the 
edges  of  the  undestroyed  strata  expose  themselves  all 
around  the  border  of  the  basin.  Then  the  rains  running 
down  the  slopes  have  worn  them  into  forms  resembling 
columns  and  pinnacles.  These  regions  are  generally  sterile, 


TO    CLAIBORXE,  ALABAMA.  177 

and  the  first  explorers  of  them  named  them  "bad  lands." 


FIG.  73. — VIEW  IN  THE  BAD  LANDS  OF  NEW  MEXICO.    (Cope.) 

Here  in  Figure  73  is  a  view  of  some  isolated  columns  stand- 
ing in  one  of  the  "  bad  lands  "  of  New  Mexico. 

EXERCISES. 

What  states  are  completely  covered  by  Tertiary  ?  What  ones 
are  more  than  half  covered  ?  What  ones  containing  Tertiary  are 
less  than  half  covered?  What  states  afford  no  good  quarry 
stones  ?  What  are  the  nearest  good  building  stones  for  use  in 
Florida?  What  is  that  singular  material  sometimes  used  for 
building  at  St.  Augustine,  Florida  ?  Would  the  "  White  Lime- 
stone "  of  Alabama  make  a  good  building  stone  ?  Could  New 
Orleans  obtain  granite  by  the  Mississippi  River  ?  Where  would 
that  city  send  to  get  granite  by  ocean  navigation  ?  Where  does 
New  Orleans  obtain  lime  ?  Can  you  think  of  any  mineral  pro- 
ductions more  convenient  to  Mobile  than  to  Boston  ?  What 
formations  were  worn  down  to  furnish  Tertiary  material  in  South 
Carolina?  Which  way  did  the  rivers  run  in  South  Carolina 
when  the  Tertiary  beds  were  forming  ?  State  what  rivers  along 
the  Atlantic  coast  existed  in  whole  or  in  part  during  Tertiary 
time.  State  what  rivers  along  the  Gulf  coast  did  not  exist  in 
Tertiary  time.  Trace  the  shore  of  the  Gulf  and  Atlantic  during 
Tertiary  time.  What  states  did  not  then  exist  as  dry  land  ? 


178  GEOLOGICAL   EXCURSIONS. 

What  states  were  then  partly  sea  bottom  ?  Is  it  supposable  that 
the  Atlantic  Tertiary  border  ever  extended  beyond  New  Jersey 
so  as  to  form  a  border  to  New  England  ?  If  so,  what  has  become 
of  those  Tertiary  deposits  ?  Does  the  Tertiary  on  Martha's  Vine- 
yard throw  any  light  on  this  question  ?  Why  do  we  find  no 
Tertiary  in  Ohio  ?  Should  there  not  be  Tertiary  around  the 
border  of  the  "  Great  Lakes,"  as  well  as  along  the  Atlantic 
border?  Where  was  the  mouth  of  the  Mississippi  in  Tertiary 
time?  Why  is  it  so  much  further  south  at  present?  What 
rivers  flow  across  the  great  Tertiary  areas  of  the  Northwest  ? 
Did  those  rivers  exist  in  Tertiary  time?  Did  any  of  them  partly 
exist  ?  Did  any  water  escape  from  the  Tertiary  inland  seas  into 
the  Atlantic  Ocean  ?  Point  out  the  course  it  may  have  pursued. 
Are  there  any  mountains  in  the  Tertiary  regions  of  the  United 
States  ?  Why  are  Tertiary  rocks  less  hard  than  Palaeozoic  rocks? 


EXCUBSION  XXX.— To  the  River  Valley. 
Quaternary  Formations. 

The  great  Drift  formation  is  almost  everywhere  present. 
We  began  with  a  study  of  the  rocks  of  the  Drift,  and  now, 
having  learned  something  of  the  deeper-lying  formations, 
we  come  back  to  the  Drift,  to  study  it  in  a  more  general 
way.  Most  other  formations  began  as  sediments  deposited 
in  bodies  of  water;  the  Drift  generally  could  not  have  had 
such  an  origin,  though  moving  water  undoubtedly  has  done 
much  in  the  arrangement  of  the  materials. 

Now  look  around  us.  Every  field  is  covered  with  a 
mass  of  subsoil  material.  In  some  cases  we  know  that  it 
is  only  a  few  feet  to  hard  rocks  below ;  but  in  most  places 
we  are  sure  it  is  many  feet.  All  our  cellars  and  wells  are 


TO   THE    RIVER    VALLEY.  179 

dug  in  this  unconsolidated  subsoil  deposit.  In  some  places 
we  find  it  quite  clayey ;  in  others  it  is  sandy ;  in  some 
others  it  is  gravelly.  Almost  everywhere,  if  we  dig  deep, 
we  shall  find  sand  and  gravel  and  clay.  Almost  everywhere, 
also,  we  shall  see  cobble  stones  and  larger  boulders  lying 
on  the  surface  or  buried  beneath  it.  Fine  examples  are 
shown  in  the  cuts,  Figures  3  and  2,  while  the  large  boulder 
of  Figure  1  may  here  be  recalled  to  mind.  These  deposits 
belong  to  the  Drift  formation.  The  kinds  of  rocks  and 
minerals  to  be  found  in  the  boulders  we  have  already 
studied  sufficiently  for  the  present. 

Suppose  we  travel  from  Canada  to  the  Gulf  of  Mexico, 
and  study  the  Drift  all  the  way.  We  shall  observe  two 
particulars  in  which  the  northern  Drift  differs  from  the 
southern.  1.  The  northern  Drift  abounds  in  boulders  ;  the 
southern  Drift  has  none.  2.  The  northern  Drift  ends 
abruptly  downward,  and  rests  on  a  smooth  hard  surface 
of  bed-rock,  as  a  rule  ;  the  southern  Drift  passes  by  gradual 
transition  from  its  sandy  or  gravelly  condition  to  a  decaying 
condition  of  the  underlying  strata.  That  is,  in  the  south, 
the  lower  part  of  the  surface  deposits  seems  to  have  resulted 
from  the  decay  of  the  underlying  strata,  and  one  can  trace 
the  stratification  upward  from  the  unaltered  rock  into  the 
overlying,  unconsolidated  beds.  These  lower  portions  have 
~been  formed  where  they  lie ;  only  the  higher,  gravelly  por- 
tions have  been  brought  from  some  other  region.  The 
lower  portions,  therefore,  are  not  .properly  any  part  of 
the  Drift.  The  upper,  transported  sand  and  gravel  are 
much  less  abundant  than  the  proper  Drift  of  the  north  ; 


180 


GEOLOGICAL  EXCUKSIOKS. 


but  yet,  in  some   localities   are  one   or  two  hundred  feet 
deep. 

Now  look  at  the  bottom  of  the  Drift  in  the  northern 
states.  The  underlying  strata  are  not  seen  partially  decayed 
and  passing  upward  into  the  condition  of  soft  loam.  They 
show  a  well  defined  upper  surface.  It  is  a  hard  surface. 
If  ever  there  were  any  decayed  portions,  they  have  been 
removed.  But  the  most  striking  fact  is  the  smoothed  con- 
dition of  this  rock  surface.  It  looks  as  if  it  had  been  planed 
down  by  some  mighty  power.  It  has  not  only  been  levelled 
and  smoothed;  it  lias  been  scratched  and  grooved  along 
straight  lines  running  in  a  general  north  and  south  direc- 
tion. There  is  no  rock  so  hard  as  to  have  resisted  this 
action.  In  New  England  and  in  the  Canadian  regions  we 


FIG.  74. — A  STRIATED  DOME  OF  QUARTZITE,  FRAZER  BAY,  LAKE  HURON. 
(Photograph  furnished  by  Dr.  E.  Andrews.) 


TO   THE   RIVER   VALLEY.  181 

find  the  most  flinty  rocks  as  perfectly  smoothed  and  striated 
as  the  softer  limestones  of  other  regions.  Dr.  E.  Andrews, 
of  Chicago,  has  photographed  an  interesting  example,  which 
you  see  reproduced  in  Figure  74.  A  dome-like  protrusion 
of  quartzite,  rising  above  the  level  of  the  water  at  Frazer 
Bay,  north  of  Lake  Huron,  has  been  planed  and  striated 
by  some  tremendous  power.  The  smoothed  rock  can  be 
traced,  extending  down  under  the  water  a  great  distance. 
Such  phenomena  are  common  along  the  Eozoic  shores  of 
the  upper  lakes.  Another  striking  example  may  be  seen 
at  Marquette.  These  facts  are  very  impressive  and  very 
important.  They  seem  to  be  connected  with  the  history 
of  the  Drift. 

In  the  Northern  States  we  can  everwhere  notice  in  the 
Drift  a  distinction  of  another  kind.  Nearly  all  the  surface 
portion  of  the  Drift  is  partially  stratified.  This  is  shown 
in  Figures  5  and  6.  This  confused  stratification  must  have 
resulted  from  the  action  of  water  in  motion.  The  deeper 
portions  of  the  Drift  are  unstratified.  They  consist  of  a 
great  mass  of  blue  clay  with  imbedded  boulders.  The  semi- 
stratified  portion  is  called  Modified  Drift,  and  the  deeper, 
unstratified  portion  is  sometimes  called  Till. 

All  around  the  shores  of  the  Great  Lakes  we  find  still 
another  condition  of  the  surface  deposits.  They  are  dis- 
tinctly and  evenly  stratified,  as  if  laid  down  in  standing 
water.  They  consist  of  fine  sand  and  clay,  without  cobble- 
stones or  large  boulders.  These  stratified  deposits  extend 
inland  from  the  lake  shore  far  enough  to  attain  an  elevation 
of  one  or  two  hundred  feet  above  the  lakes.  There  they 


182  GEOLOGICAL   EXCURSIONS. 

terminate,  and  the  surface  beyond  consists  of  the  usual 
Modified  Drift.  It  looks  as  if  the  water  of  the  lakes  had 
once  stood  high  enough  to  cover  these  low  border  deposits, 
and  had  laid  them  down  in  the  usual  method  of  sedimenta- 
tion. These  beds,  therefore,  are  not  properly  a  part  of  the 
Drift.  The  several  strata  descend  gradually  toward  the 
lake,  and  apparently  pass  under  the  lake.  As  their  out- 
crops are  at  higher  levels  than  any  part  of  the  surface 
nearer  the  lake,  it  happens  that  artesian  wells  are  some- 
times attained  by  boring  into  them. 

When  the  lakes  stood  at  the  high  levels  indicated  by 
these  lacustrine  deposits,  they  formed  gravel  beaches  around 
their  borders.  Beaches  were  formed  at  various  elevations 
during  the  progress  of  the  lowering  of  the  lakes.  These 
beaches  still  exist,  and  may  be  traced  around  nearly  all  the 
lake  borders.  We  call  them  Lake  Terraces. 

Terraces  also  border  many  of  our  rivers.  They  seem 
to  have  been  formed  when  the  rivers  flowed  at  higher  levels 
than  at  present.  Here,  in  Figure  75,  is  a  section  across  a 


FIG.  75. — SECTION  ACROSS  A  TERRACED  RIVER  VALLEY. 

river  valley,  showing  terraces  at  three  different  levels  on 
one  side,  and  four  different  levels  on  the  other.  The  main 
valley  is  seen  excavated  in  4he  underlying  solid  rocks. 
Then,  when  the  river  flowed  at  the  height  ^yand  e'  f ,  it 


TO   THE   RIVER   VALLEY.  183 

formed  the  upper  terrace.  This  may  be  one,  two  or  three 
hundred  feet  above  the  present  river  level.  At  a  later 
time,  when  the  river  level  had  subsided,  it  formed  the 
lower  terraces  c  d  and  c'  df.  The  intermediate  terrace  /•, 
on  one  side,  has  been  destroyed  on  the  other  side.  At 
the  present  time  the  river  has  shrunken  so  as  only  to  till 
the  channel  R,  and  when  it  overflows  its  banks,  it  throws 
its  sediment  down  on  the  flood  plains  a  b  and  a'  bf. 

There  must  have  been  some  powerful  cause  for  the 
former  high  level  of  the  lakes  and  rivers.  The  rivers  could 
have  been  flooded  by  a  former  greater  abundance  of  water. 
The  lake-levels  would  have  been  raised  also,  to  a  limited 
extent,  by  the  same  cause  ;  but  to  raise  the  Great  Lakes 
one,  two  or  three  hundred  feet,  there  must  have  been  some 
great  barrier  at  the  outlet  of  the  lakes,  which  dammed  the 
waters.  One  barrier,  I  think,  was  at  the  termination  of 
the  Niagara  gorge,  as  shown  in  Figure  58,  page  142.  The 
dotted  lines  there  show  the  former  level  of  the  lakes. 

If  the  Great  Lakes  have  fallen  as  much  as  the  high 
terraces  indicate,  it  is  easy  to  understand  that  small  lakes 
may  have  been  completely  drained,  or  completely  filled  up 
with  sediments.  Figure  20  shows  this  filling  in  progress. 
This  would  take  place  during  the  same  period  when  the 
terraces  were  forming. 

Some  other  conditions  of  the  surface  formations  exist 
in  some  regions,  but  these  principal  ones  are  all  which  we 
need  study  at  present.  All  these  modified  states  of  the 
transported  Drift  materials  have  been  called  Champlain 


184  GEOLOGICAL   EXCURSIONS. 

Deposits,  and  the  period  of  their  formation,  the  Champlain 
Period. 

Now  let  us  summarize  the  succession  of  surface  mate- 
rials, as  far  as  described : 

QUATERNARY  FORMATIONS. 
Unconsolidated  Surface  Materials. 
Northern  States.  Southern  States. 

Terrace  Formation,  including  Beds    Terrace     Formation     [including 
of   Marl  and  Peat   [also  L5ss,  Loss,  Orange  Sand,  etc], 

etc]. 
Lacustrine  Deposits. 

Modified  Drift,  Modified  Drift, 

with  Boulders.  without  Boulders. 

Till.  [No  Till.] 

Striations  on  Rock-surfaces.  [No  Striations  on  Rock-surfaces.] 

[Decaying  Strata  removed.]  Decaying  Strata  in  place. 

Unaltered  Rocks.  Unaltered  Rocks. 

EXERCISES. 

How  does  the  Drift  formation  differ  from  a  Sandstone  forma- 
tion ?  Is  the  Drift  a  proper  sediment  ?  How  is  it  unlike  a  sedi- 
ment ?  What  has  water  had  to  do  with  this  formation  ?  Was  it 
still  water,  or  water  in  motion  ?  Did  the  action  of  this  water 
extend  over  the  Southern  States  as  well  as  the  Northern  ?  Did 
the  action  of  this  water  affect  the  whole  thickness  of  the  Drift  in 
the  Northern  States?  Why  do  you  give  this  answer?  Did  the 
action  of  the  water  affect  the  whole  thickness  of  the  Drift  in  the 
Southern  States?  What  portion  of  the  Drift  has  been  trans- 
ported? Mention  some  kinds  of  rocks  found  in  the  Drift.  »Are 
such  rocks  Mesozoic  or  Palaeozoic  ?  Do  we  have  crystalline  rocks 
in  the  Mesozoic  or  Palaeozoic  ?  Do  we  have  them  in  the  Eozoic  ? 
Where  may  we  find  Eozoic  rocks  existing  as  the  bed-rocks? 
In  what  direction  are  the  Eozoic  rocks  from  the  Middle  States  ? 
From  what  direction,  then,  have  our  boulders  been  transported  ? 
Do  the  scratches  on  the  rock  surfaces  under  the  Drift  indicate 


TO   SWITZERLAND.  185 

transportation  from  the  direction  which  you  last  mentioned  ? 
Is  there  any  reason  for  concluding  that  our  boulders  have  not 
all  come  from  New  England  ?  Are  there  none  but  hard  and 
crystalline  rocks  north  of  the  Middle  States  ?  Why  are  there  so 
few  sandstones  and  limestones  among  the  boulders  ?  What  sorts 
of  rocks  would  be  slowly  dissolved  in  the  soil?  Would  that 
result  in  a  benefit  or  an  injury  to  the  soil  ?  Did  the  Connecticut 
River  exist  before  the  Drift  was  laid  down  ?  How  did  it  compare 
in  size  with  the  present  Connecticut?  Can  you  think  of  any 
evidence  that  the  land  once  extended  farther  south  at  New  York 
than  it  does  at  present?  Look  on  the  Geological  Map,  and 
notice  the  dotted  lines  off  the  mouth  of  the  Hudson  River,  and 
try  to  think  what  they  signify.  Why  are  they  so  notched  north- 
ward? If  the  Great  Lakes  ever  stood  200  feet  higher  than  at 
present,  what  are  some  of  the  cities  whose  sites  were  covered  by 
the  water?  Could  the  lakes  then  have  had  any  other  outlet  than 
the  present  one? 


EXCURSION  XXXI.—  To  Switzerland. 
About  Glaciers. 

You  have  learned  the  main  facts  about  the  Quaternary 
deposits.  We  cannot  attempt  now  to  study  very  thoroughly 
the  way  in  which  these  results  have  been  produced.  Let  me 
only  say  that  geologists  are  of  the  opinion  that  the  whole 
country  was  once  covered  by  a  great  glacier,  as  far  south  as 
the  boulders  extend.  It  is  likely  the  surface  was  already 
deeply  covered  with  decayed  rock-material,  such  as  still 
exists  in  the  Southern  States.  As  all  glaciers  move,  this 
great  glacier  moved  southward.  It  shoved  along  much  of 
the  loose  decayed  material,  and,  in  doing  so,  smoothed  and 
striated  the  sound  rock-surface  underneath.  The  glacier 


186  GEOLOGICAL   EXCURSIONS. 

only  extended  south  as  far  as  the  Ohio  River,  except  in  the 
elevated,  cooler  region  of  the  Appalachians.  After  some 
ages,  there  was  another  change  of  climate,  and  the  ice  was 
melted.  Great  floods  carried  sand  and  gravel  over  the 
Southern  States.  At  a  later  epoch,  the  water  still  flooded 
the  rivers,  and  at  this  time  the  high  river  terraces  were 
formed.  By  degrees  the  ice  disappeared  ;  the  lower  terraces 
were  formed  ;  small  lakes  were  becoming  drained;  beds  of 
marl  and  peat  were  forming,  and  the  conditions  of  modern 
times  approached.  So  we  stand  just  at  the  outcome  of  great 
events  which,  in  remoter  times,  transformed  the  surface  of 
the  whole  country. 

Geologists  think  a  good  deal  of  light  is  thrown  on  the 
origin  of  boulders  and  Drift  by  what  may  be  seen  in  countries 
where  glaciers  still  exist.  A  glacier  is  a  mass  of  ice  which 
has  resulted  from  the  softening  and  change  of  snows  which 
have  lain  a  long  time.  You  have  seen  the  ice  on  the  side- 
walk or  in  the  gutters,  which  has  resulted  from  partially 
melted  snow —  especially  when  spring  is  approaching.  Such 
ice  is  glacier-like  in  character  and  origin.  The  great 
glaciers  last  all  summer,  and  continue  from  year  to  year. 
So  they  can  only  exist  in  regions  with  a  cool  climate  and 
plenty  of  snow  fall.  The  best  known  glaciers  in  our  time 
are  those  which  occupy  the  valleys  of  the  Alps.  In  the  cut, 
Figure  76,  are  two  glaciers  seen  flowing  along  valleys  which 
lead  upward  toward  the  summit  of  Mont  Blanc.  The  one 
in  the  middle  of  the  view  is  called  Glacier  des  Bossons 
(Glacier  of  Bossons,  a  little  village  at  its  foot),  and  the  one 
on  the  right  is  the  Glacier  de  Taconnay.  Every  glacier  in 


TO   SWITZEKLAKD, 


187 


its  course  gathers  up  a  great  amount  of  rock  rubbish,  and 
deposits  it  in  a  long  ridge  each  side.  These  ridges  are 
called  lateral  moraines.  Another  mass  is  deposited  at  the 


FIG.  76. — VIEW  OF  A  COUPLE  OF  GLACIERS  FLOWING  DOWN  FROM  MONT  BLANC. 

termination  of  the  glacier.  This  is  the  terminal  moraine. 
In  this  cut  you  can  see  something  of  the  terminal  moraine 
about  the  foot  of  both  glaciers.  It  is  made  up  of  boulders 
and  clay. 

But  a  more  remarkable  sight  is  shown  in  the  cut,  Figure 
77,  which  is  a  vast  boulder-strewn  area  at  the  foot  of  Glacier 
des  Bois,  which  is  only  the  lower  part  of  the  Mer  de  Glace 
or  Sea  of  Ice.  (Bois  is  the  name  of  a  little  village  at  its 
foot.)  On  the  extreme  right  is  a  portion  of  the  vast  moraine 
which  borders  the  left  side  of  the  glacier,  and  continues 


188 


GEOLOGICAL   EXCURSION'S. 


around  to  form  part  of  the  terminal  moraine  —  in  the  same 
way  as  seen  in  Figure  76.  Beyond  this  appears  the  white 
termination  of  the  glacier,  with  some  boulders  resting  on  its 
back.  The  terminal  face  of  the  glacier  is  turned  toward 
us,  and  a  large  arch  opens  at  its  base  into  a  dark  passage, 
from  which  a  roaring,  muddy  stream  of  water  rushes.  There 


PIG.  77. —  BOULDER-STREWN  AREA  AT  THE  FOOT  OP  THE  MER  DE  GLACE, 
VALLEY  OF  CHAMONIX.     Compare  the  Boulder  Field  shown  in  Figure  8. 

are  in  fact  two  streams,  and  these  unite  to  form  the  Arvey- 
ron,  which,  a  little  further  on,  unites  with  the  Arve.  The 
glacier  extends  toward  the  right  far  up  to  the  same  snow- 
covered  summit  of  Mont  Blanc  from  which  we  see  the  two 
other  glaciers  proceeding  in  the  last  cut.  At  the  very  ter- 
mination of  this  glacier,  it  is  therefore,  turned  suddenly  to 
the  left.  This  is  to  avoid  the  enormous  mass  of  rock  which 
lies  exactly  in  the  main  course  of  the  glacier.  This  rock  is 
shown  next  beyond.  It  is  a  dome  of  porphyry,  smoothed 
and  striated  much  like  the  quartzite  dome  shown  in  Figure 


TO   SWITZERLAND.  189 

74.  The  glacier,  some  years  ago,  was  nearly  a  thousand 
feet  higher  than  at  present,  and  flowed  completely  over  this 
porphyry  obstacle.  It  was  the  glacier  which  smoothed  and 
striated  its  surface.  This  convinces  us  that  the  quartzite 
dome  on  the  north  shore  of  Lake  Huron  may  have  been 
smoothed  and  striated  by  a  glacier.  But  glancing  again  at 
Figure  77,  you  can  see  beyond  the  porphyry  mass,  the  great 
lateral  moraine  rising  up.  This  continues  down  and  con- 
nects with  the  vast  terminal  moraine  shown  at  the  left  of 
our  cut. 

There  are  men  living  at  that  place  who  remember  when 
the  glacier  was  984  feet  higher  than  at  present,  and  extended 
1640  feet  farther,  and  at  that  time  made  the  great  terminal 
moraine  which  still  remains,  and  rises  80  feet  high.  The 
moraine  has  pushed  close  to  the  little  village  of  Bois,  which 
still  stands  close  at  its  foot.  Some  of  the  huge  boulders 
rolled  down  among  the  houses  and  the  people  were  greatly 
terrified.  It  was  in  1826  that  the  glacier  was  so  much  larger 
than  at  present.  Since  that  time  the  glacier  has  retreated 
across  the  boulder-strewn  area  which  we  see,  and  has  pro- 
duced a  scene  which  reminds  us  strongly  of  the  boulder  field 
shown  in  Figure  3. 

If  this  glacier  should  continue  to  melt  away  until  it  dis- 
appears, the  great  moraines  would  remain.  Now,  we  find 
in  America  many  ridges  of  gravel  and  boulders  so  much  like 
the  Alpine  moraines  that  we  call  them  real  moraines,  and 
believe  that  there  were  once  glaciers  which  formed  them.  In 
fact  we  often  find  them  stretching  across  the  foot  of  a  valley 
which  could  have  been  once  filled  with  glacier  ice.  But 


190  GEOLOGICAL   EXCURSIONS. 

there  are  so  many  which  extend  for  long  distances  that  the 
only  explanation  seems  to  be  that  the  whole  country  was 
once  covered  by  glaciers.  If  this  theory  is  correct, 
then  we  are  to  think  of  these  beautiful  fields  and  valleys, 
which  are  now  the  home  of  a  busy  and  happy  population,  as 
once  covered  by  a  sheet  of  ice  as  deep,  as  bleak  and  ver- 
dureless  as  that  which  in  our  times  covers  the  whole  of 
Greenland. 

EXERCISES. 

Is  there  any  part  of  the  world  where  the  snow  does  not  dis- 
appear in  summer  ?  Why  does  it  not  disappear  on  high  moun- 
tains ?  Is  there  no  thawing  on  high  mountains  in  summer  ?  Does 
it  ever  thaw  in  the  Arctic  regions  ?  Is  it  conceivable  there  might 
be  so  little  snow  in  any  Arctic  region,  as  to  all  melt  in  the  summer? 
What  is  meant  by  the  limit  of  perpetual  snow  ?  In  what  zone  is 
this  limit  highest  ?  Why  may  it  be  higher  on  some  mountains 
than  on  other  mountains  in  the  same  latitude  ?  Is  the  climate 
always  too  cold  for  farm  crops  in  the  neighborhood  of  Alpine 
glaciers  ?  How  close  to  the  foot  of  a  glacier  may  gardens  be 
planted  ?  Why  is  there  a  cold  stream  of  air  descending  from  the 
surface  of  a  glacier  ?  Are  all  the  glaciers  of  the  Alps  retreating 
like  the  Glacier  des  Bois  ?  How  much  further  down  the  valley 
of  the  Alps  may  the  Alpine  glaciers  have  extended  formerly  ? 
Are  there  any  glaciers  in  the  United  States  ?  If  so,  where  are 
they  ?  Is  it  supposable  there  were  ever  glaciers  in  the  White 
Mountains,  the  Green  Mountains  and  the  Alleghanies  ?  What 
evidences  of  this  would  you  expect  ?  Was  the  climate  any  colder 
then,  or  were  the  glaciers  simply  caused  by  a  greater  amount  of 
snow  fall  ?  How  much  of  our  country  was  covered  with  ice  at 
that  time  ?  How  far  south  did  the  ice  extend  ?  How  can  we  tell 
how  far  south  it  extended  ?  What  was  the  appearance  of  the 
country  at  that  time  ?  What  distinguished  scientist  penetrated 
to  the  centre  of  Greenland  in  1883  ? 


THROUGH   THE   AGES.  191 

EXCURSION  XXXII.— Through  the  Ages. 
About  the  Plants  and  Animals  of  the  Past. 

Let  us  now,  finally,  in  imagination  travel  down  through 
the  Ages  of  the  world's  history,  and  note  the  appearances 
from  time  to  time  assumed  by  our  planet  and  its  popula- 
tions. Everything  in  geology  indicates  that  the  world  is 
very  old,  and  has  undergone  many  remarkable  changes. 
It  is  generally  believed  that  it  once  existed  in  the  form 
of  an  intensely  heated  vapor,  but  we  will  say  nothing  about 
that.  We  are  pretty  certain  that  it  was  once  a  globe  of 
melted  mineral  matter,  and  that  after  a  long  time,  cooling 
caused  a  crust  to  form  over  the  surface.  At  a  later  period, 
clouds  of  watery  vapor  first  came  into  existence,  and  tor- 
rents of  rain  poured  down  during  many  ages.  "When  the 
clouds  were  exhausted,  the  earth  was  covered  by  a  film  of 
water.  It  was  a  universal  ocean.  After  many  ages  more, 
sea  weeds  were  in  existence  in  the  ocean.  Whence  they 
came  nobody  knows.  By  and  by  some  long  ridges  of  sea 
bottom  rose  above  the  ocean  level,  and  became  the  begin- 
nings of  solid  land.  The  sea  weeds  floated  to  the  beach  in 
immense  piles,  and  were  buried  beneath  sediments  which 
resulted  from  the  wear  of  the  land  and  from  chemical 
precipitations.  In  course  of  time  they  were  changed  to 
plumbago  —  and  here  is  some  of  that  plumbago  in  the  pencil 
with  which  you  write. 

Ages  later,  the  first  animals  appeared.  Their  origin  is 
another  unsolved  problem.  They  were  simple  gelatinous 
forms,  with  scarcely  any  special  organs ;  but  they  existed  in 


192 


GEOLOGICAL   EXCURSIONS. 


cv 


portion  in  a  contracted  state,  c  c,  two  pseudo- 
pods  closing  around  an  infusorian  (  Urocentrum). 
a,  diatoms  within  the  animal.  &,  particle  of 

sawdust. 


immense  numbers,  and 
thousands,  probably 
millions,  of  them  grew 
in  one  mass,  and  secret- 
ed great  reefs  of  lime- 
stone, much  like  coral 
reefs.  In  Figure  78 
are  seen  modern  repre- 
sentatives of  these  crea- 
tures. They  are  not 

grown  together  like  the 
FIG.  78.  —  A  LIVING  REPRESENTATIVE  OF  THE 

OLDEST  ANIMAL.    Amo&ba  proteus  (after   ancient    ones,    and     do 
Leidy).  not   secrete   any   coral- 

n,  nucleus,     c  v,  contractile  vesicle,     «,  posterior    I--L  "Kafon^n  "R  if 

11KG 

their     iglly-like      bodies 

are  believed  to  be  sim- 
Magnifled  100  diameters  in  the  upper  spe-    -lar    to    the    bod       sub_ 
cimen,  and  125  in  the  lower.     Found  fre- 
quently in  fresh  waters.  stance    of    the    ancient 

ones.    These  earliest  of 

animals  lived  during  the  Eozoic  Time.  When  Palaeozoic 
Time  began,  considerable  advance  had  been  made  in  sea 
weeds,  and  much  more  in  animal  life.  We  find  in  the 
rocks  many  remains  of  creatures  related  to  lobsters  and 
crabs,  but  very  much  lower  in  rank.  We  call  them  Trilo- 
bites.  (See  Figure  79.)  With  them  were  many  molluscs 
related  to  the  Pearly  Nautilus,  but  most  of  them  were 
straight  instead  of  coiled.  Their  shells  were  chambered. 
The  animal  lived  in  the  outer  chambej?.  Some  of  the 
shells  grew  to  a  length  of  ten  or  fifteen  feet.  Figure  80 


THROUGH   THE   AGES. 


193 


shows  one  of  these  straight-chambered 
shells.  It  belongs  to  the  genus  OrtkoOe- 
ras  (Orthoc'-e-ras).  These  rapacious  beings 
were  the  monarchs  of  the  sea.  There 
were  indeed  other  molluscs  somewhat 
like  our  modern  bivalves  and  univalves, 
but  none  of  them  was  identical  with 
any  living  species.  The  older  creatures 
in  all  cases  were  simpler  in  their  organi- 
zation. 

In  the  Devonian  Age  there  was  more 
land.  It  supported  forests  of  curious  trees 
which  bore  no  flowers.  Some  of  them 
were  much  like  modern  Club  Mosses. 
We  call  this  kind  of  tree  Lepidodendron. 
A  view  of  one  is  presented  in  Figure  67. 
Many  coral-making  animals  flourished ;  arid 
the  Trilobites  and  all  the  classes  of  mol- 
luscs just  mentioned  continued  to  flourish.  The  most 
important  thing  was  the  first  appearance  of  vertebrated 
animals  —  that  is,  those  having  a  back-bone.  They  were 
fishes.  Nature  always  begins  with  the  lowest  forms  and 


FIG.  79.— A  TRILO- 

BITE   FROM    THE 

SILURIAN.  The 
upper  figure 
shows  the  ani- 
mal rolled  up. 


FIG.  80, — RESTORATION  OF  AN  ORTHOCERAS — A  STRAIGHT -CHAMBERED 

SHELL  OF  PALAEOZOIC  TIME. 
a.  arms ;  /,  funnel ;  c,  chamber ;  s,  siphuncle. 


194 


GEOLOGICAL  EXCUKSIONS. 


FIG.     81.  —  PTERICHTHYS 


works  upward.  But  they  were 
exceedingly  singular  fishes,  and 
one  might  almost  call  some  of 
them  by  other  names.  Figure 
81  shows  a  specimen  from  the 
Devonian  rocks  of  Scotland,  and 
Figure  82  a  specimen  from  the 
Devonian  strata  of  Ohio.  Each 
of  these  appears  to  have  been 

WINGED    FISH   (after   Pan-     twenty  or  thirty  feet  in  length, 
der).      From   the  Devonian      Tj          were  ^     fc 

of  Scotland. 

bony  plates,    instead   of  horny 

scales.  The  Ohio  fish  had  a  head  three  feet  long  and  two 
feet  broad.  The  jaws  were  armed  with  terrible  teeth. 
These  fishes  must  have  been  in  their  time  the  cruel  tyrants 
of  the  Devonian  Ocean. 

So  things  went  on  in  the  sea  during  Carboniferous  times. 
But  the  straight-chambered  shells  dwindled  away.  So  did 
the  Trilobites.  But  coiled-chambered  shells  gradually  took 
the  place  of  the  first,  and  higher  crustaceans  (like  lobsters 
and  craw-fishes)  the  place  of  the  latter.  The  fishes  were 


FIG.  82.— DINICHTHYS  OR  TERRIBLE  FISH  (Newberry).     From  the  Devonian 

of  Ohio. 


THKOUGH   THE   AGES. 


195 


much  improved,  but  they  were  mostly  after  the  fashion  of 
the  bony-scaled  gar-pikes.  The  great  characteristic  of  the 
Carboniferous  age  was  the  increase  of  land  vegetation.  But 
it  was  still  flowerless,  and  most  of  it  resembled  vegetation 
which  had  begun  to  nourish  in  the  Devonian.  Views  of 
some  kinds  may  be  seen  in  Figures  66,  67  and  68.  It 
luxuriated  over  vast  expanses  which  were  little  above  sea- 
level,  and  were  many  times  submerged  by  the  frequent 
changes  in  the  elevation  of  the  land.  The  forests  thus  sub- 
merged did  not  go  to  decay,  but  were  changed  into  the  coal 
which  we  burn  in  our  fires.  There  were  no  men  to  use  the 
timber  when  it  grew ;  therefore  it  was  laid  away  to  wait  till 
mankind  should  arrive. 

After  the  coal  was  laid  away,  the  Appalachian  Mountains 
were  uplifted,  and  nature  now  introduced  a  great  many 
changes.  This  was  now 

the  Mesozoic  Time.  JlKMRl  "  fill' 
Flowering  plants  now 
first  appeared.  The 
coiled-chambered  shells 
became  more  beautiful 
and  more  complicated. 
Most  of  them  belonged 
to  the  type  of  Ammon- 
ites. Here  is  one  in 
Figure  83.  Notice  that 
the  interior  is  divided  into  chambers  by  cross  partitions  or 
septa  which  are  very  much  folded.  The  old  kinds  of  bi- 
valves belonging  to  the  type  of  lamp-shells  —  called  BracM- 


FIG.   83. — AN    AMMONITE    OF    MESOZOIC 

TIME.     Ammonites  serpentinus,  Schl. 

a,  Side  view.    6,  Edgewise  view    c,  Plan  of  septa 

lobes. 


196 


GEOLOGICAL  EXCURSIONS. 


opods — disappeared,  and  only  the  modern  kinds  remained. 
Fishes  with  bony  skeletons  and  horny  scales  came  into 
existence.  This  is  the  type  of  our  common  fishes.  Most 
important  of  all,  air-breathing  animals  dwelt  on  the  land 
and  in  the  water.  They  had  begun  to  exist  during  Coal 
Measure  times,  but  the  vertebrates  were  related  to  Amphib- 
ians. These  vertebrates  were  Reptiles.  They  were  the 


FIG.  84. —  REPTILES  OF  MESOZOIC  TIMES.     (Hawkins.) 

highest  in  existence  on  the  earth.  They  presented  a  won- 
derful amount  of  diversification  among  themselves.  They 
were  suited  to  live  in  the  ocean,  the  river,  on  the  land  or  in 
the  air.  They  could  walk  or  crawl,  swim  or  fly.  Some 
went  on  four  legs,  some  could  walk  on  two.  In  Figure  84 
some  of  these  strange  types  are  shown.  Figure  85  shows 
the  skeleton  of  a  reptile  which  could  walk  like  a  bird  on 
two  feet,  and  had  also  foot  and  ankle  bones  closely  resem- 
bling those  of  birds.  At  the  same  time  there  were  birds 
which  resembled  reptiles  in  some  respects.  One  European 


THItOUGH   THE   AGES. 


197 


bird  had  a  long  vertebrated  tail 
like  that  of  a  lizard,  but  quills 
projected  from  each  side.  Other 
birds  in  America  resembled  rep- 
tiles by  having  teeth  in  their 
jaws.  In  fact,  the  European  bird 
probably  had  teeth  also.  All 
through  this  time,  the  ocean 
stretched  in  America  from  the 
Gulf  of  Mexico  through  the 
centre  of  the  continent  to  the 
Arctic  Ocean. 


Next,    nature    introduced    an-    FIG.  85.— A  BIPEDAL  REPTILE 


other  great  change.  The  central 
regions  of  the  continent  were  up- 
lifted. The  great  central  ocean 

parted.  One  branch  shrank  to  the  Gulf  of  Mexico  and 
the  other  to  the  Arctic  Ocean.  Some  of  those  great 
interior  seas  remained,  whose  places  are  now  marked  by 
the  "Bad  Lands"  of  the  Far  West.  This  was  the  Ter- 
tiary Age  of  Ceenozoic  Time.  But  the  most  important 
changes  were  among  the  animals.  Now  mammals  became 
very  abundant.  These  are  vertebrates  which  give  milk. 
There  had  indeed  been  a  very  few  mammals  in  Mesozoic 
Time ;  but  now  they  swarmed.  Like  the  fishes  when  they 
first  appeared,  the  mammals  were  very  peculiar,  and  many 
of  them  were  large.  We  could  say  that  they  bore  remote 
resemblances  to  modern  mammals;  but  the  striking  pecu- 
liarity was  that  the  same  animal  bore  resemblances  to  two. 


OF  MESOZOIC  TIME.  Had- 
rosaurus.  (After  Haw- 
kins.) 


198  GEOLOGICAL   EXCURSIONS. 

three,  four  or  five  modern  mammals.  Such  animals  we 
call  comprehensive  types.  They  all  had  small  brains,  and 
there  was  a  preponderance,  in  the  earliest  epoch,  of  five- 


FIG.  86. — A  MESOZOIC  BIRD  WITH  A  REPTILIAN  TAIL.    Archceopteryx. 
(After  Owen.) 

toed  quadrupeds,  and  many  of  these  walked  with  the  whole 
length  of  the  foot  on  the  ground,  like  the  bear,  the  kangaroo 
and  man.  Figure  87  shows  one  of  the  earlier  Tertiary 


FIG.  87. — SKELETON  OF  AN  EARLY  TERTIARY  MAMMAL  OF  AMERICA.     (After 
Marsh.)    Length,  eleven  feet.     Dinoceras  mirabile,  Marsh. 


THKOUGH   THE   AGES. 


199 


forms.  In  the  course  of  ages  the  comprehensive  types  dis- 
appeared, and  new  types  took  their  place,  in  which  the 
different  characteristics  were  divided  among  different  orders. 
For  instance,  those  having  gnawing  teeth,  like  rats,  no 


FIG.  88. — A  QUATERNARY  MAMMAL  OF  AMERICA  IMMEDIATELY  BEFORE  THE 
GREAT  GLACIER.  (After  Riou.)  Megatherium  Cuvieri,  Desmarest. 
Sometimes  eighteen  feet  in  length. 

longer  had  hind  teeth,  like  the  tapir  or  the  horse.  Those 
having  five  hoofed  toes  no  longer  had  canine  teeth  like  a 
dog.  Figure  88  shows  a  form  closely  related  to  the  Eden- 
tates of  South  America.  The  Megatherium  lived  just  after 


200  GEOLOGICAL  EXCURSIONS. 

the  close  of  the  Tertiary.  So  the  aspects  of  the  animals 
continued  to  approach  nearer  to  modern  animals  ;  and  as 
the  interior  seas  became  filled,  the  face  of  the  continent 
assumed  the  appearance  it  was  destined  to  have  in  human 
times.  But  there  was  no  man  yet. 

Next  came  that  increase  of  cold  which  caused  the  won- 
derful glacier  visitation  of  which  you  have  learned.  One 
of  its  effects  was  to  renew  the  surface  of  the  earth — to 
obliterate  the  old  scars  and  gullies  caused  by  the  long 
continued  erosions  of  the  Tertiary  Age ;  to  supply  material 
for  a  new  subsoil,  and  make  everything  ready  for  man,  who 
was  to  appear  in  the  next  act  of  the  drama.  The  great 
glaciers  were  not  half  dissolved  when  man  appeared  in 
Europe.  Perhaps  he  was  in  America  quite  as  early.  It  is 
my  own  opinion  that  dark-skinned  men  had  been  in  exist- 
ence in  the  tropical  regions  during  the  whole  glacial  period, 
and  perhaps  much  longer.  But  you  are  not  to  consider  this 
settled.  It  is  also  my  opinion  that  the  first  people  in 
Europe,  as  well  as  America  and  Asia,  were  yellow-skinned, 
and  that  the  white  race  appeared  later.  But,  whatever  may 
be  the  truth  about  these  things,  it  is  quite  certain  that  the 
first  colonists  in  Europe  were  rude,  and  that  civilization  has 
grown  up  through  the  long  struggle  of  man's  intelligence 
and  better  nature  against  the  obstacles  presented  by  his 
own  savage  disposition,  and  the  lack  of  inventions  to  aid 
him  in  the  subjugation  of  the  earth. 

After  thousands  of  years,  the  white  race  has  attained  a 
wonderful  stage  of  improvement;  and  we  should  feel 
thankful  that  our  own  lot  has  been  cast  in  these  later  times, 


THKOUGH   THE   AGES.  201 

when  we  can  enjoy  so  many  opportunities  for  acquiring 
knowledge  of  the  past  and  present,  the  distant  and  the 
near,  and  for  attaining  the  highest  culture  of  our  own  social 
and  moral  faculties. 

Now,  my  dear  pupils,  I  think  it  will  be  best  to  make 
this  the  end  of  our  series  of  Geological  Excursions.  There 
are  many  things  still  which  might  be  presented  in  a  very 
simple  way,  but  we  must  postpone  them  all  for  the  present. 
I  hope  you  have  enjoyed  these  Excursions  ;  and  I  hope  you 
already  feel  eager  to  take  a  new  start,  and  go  with  me  over 
a  more  thorough  course  in  geology. 

EXERCISES. 

Can  you  mention  any  animal  which  belongs  to  the  class  of 
Amphibians?  In  what  age  were  Amphibians  the  highest  type 
of  animals  ?  To  what  class  of  vertebrates  does  the  salamander 
belong?  What  is  the  difference  between  a  salamander  and  a 
lizard  ?  When  did  flowers  first  appear  on  the  earth  ?  Was  most 
of  the  coal  formed  from  flowering  plants  or  from  flowerless 
plants?  Mention  several  flowerless  plants  now  living  on  the 
earth.  Why  were  not  trees  the  first  plants  to  exist  ?  Which 
are  highest,  marine  plants  or  terrestrial  plants?  On  the 
whole,  was  there  an  improvement  of  organization  as  the  ages 
passed  by,  or  was  there  not  ?  What  has  been  the  best  age  in 
the  history  of  the  world  for  man  to  live  in  ?  What  has  been  the 
best  period  since  man  appeared  in  Europe  ?  What  houses  did 
the  first  European  people  inhabit  ?  What  implements  did  they 
use  ?  What  metals  were  they  ignorant  of  ?  What  crops  did 
they  neglect  to  raise  ?  Do  you  think  they  were  as  comfortable 
as  our  own  people  ?  Do  you  think  they  were  as  happy  ?  How 
have  education  and  civilization  improved  the  condition  of  man- 
kind? 


202  GEOLOGICAL   EXCURSIONS. 

QUESTIONS  ON  THE  TEXT. 

With  Additional  Exercises  Interspersed. 

[The  following  questions  maybe  used  in  a  general  review 
of  the  whole  subject.  They  may  also  be  employed  by  the 
teacher  in  connection  with  the  daily  Excursion  ;  but  it  will 
be  better  for  the  teacher  to  acquire  such  familiarity  with  the 
subject  treated  in  the  Excursion  as  to  ask  questions  suggested 
by  the  special  circumstances.  In  no  case  are  the  Exercises 
to  be  omitted,  as  these  are  not  questions  on  the  text,  but 
more  in  the  nature  of  applications  and  inferences  from  the 
facts  presented  in  the  text.  ] 

I. 

1.  What  objects  in  the  garden  do  not  grow  ?  2.  In  what  par- 
ticulars do  plants  differ  from  stones  ?  3.  How  do  plants  take 
nourishment  ?  4.  In  what  respect  is  an  animal  like  a  plant  ? 
5.  In  what  respect  does  he  differ  from  a  plant  ?  6.  What  is  an 
organic  body  ?  7.  What  is  an  organ  ?  8.  What  is  a  function  ? 
9.  Name  some  organs  of  a  tree.  10.  What  are  the  functions  of 
the  organs  named  ?  11.  What  objects  in  the  garden  have  no 
organs  ?  12.  Can  a  plant  or  an  animal  perform  functions  without 
organs  ?  13.  Which  has  more  organs,  a  bird  or  a  plant  ?  14. 
Which  has  more,  an  apple  tree  or  a  mushroom  ?  15.  What  is  an 
inorganic  body  ?  16.  Do  inorganic  bodies  perform  any  functions? 
17.  What  is  a  mineral  substance  ?  18.  Name  some  mineral 
substances.  19.  Are  organic  bodies  composed  of  mineral  sub- 
stances ?  20.  If  so,  how  do  they  differ  from  inorganic  bodies  ? 
21.  Is  a  dead  dog  organic?  22.  What  is  an  organic  product? 
23.  What  would  you  call  a  tear?  24.  Is  a  "living  spring"  or- 
ganic ?  25.  If  not,  why  not  ?  26.  Why  is  it  called  living  ? 


QUESTIONS   ON   THE  TEXT.  203 

II. 

1.  What  is  the  soil  in  the  garden  composed  of  ?  2.  What  is 
the  difference  between  a  pebble  and  a  grain  of  sand  ?  3.  What 
is  a  cobble  stone  ?  4.  How  does  it  differ  from  a  stone  broken 
out  of  a  quarry  ?  5.  What  use  is  sometimes  made  of  cobble 
stones  ?  6.  What  use  is  made  of  pebbles  and  gravel  ?  7.  How 
could  gravel  be  used  to  purify  water  ?  8.  What  is  a  boulder  ? 
9.  How  does  it  differ  from  a  pebble  ?  10.  Are  pebbles  and 
cobble  stones  boulders?  11.  What  colors  can  we  detect  in  grains 
of  sand?  12.  What  are  pebbles  made  up  of?  13.  What  dif- 
ferent colors  can  you  detect  in  the  grains  of  a  pebble  ?  14.  What 
is  each  different-colored  portion  of  a  pebble  or  cobble  stone 
called?  15.  Is  a  grain  of  sand  ever  composed  of  more  than  one 
mineral?  16.  What  is  the  indication  of  this?  17.  What  dif- 
ferent colors  of  minerals  may  be  detected  in  pebbles  and  larger 
boulders  ?  18.  What  colors  have  you  yourself  seen  ?  19.  What 
is  the  shape  of  the  separate  minerals  in  a  cobble  stone  ?  20. 
Are  the  separate  minerals  quite  distinct  from  each  other,  or  do 
they  blend  together?  21.  Are  they  always  the  same  in  this 
respect  ?  22.  Are  all  loose  stones  boulders  ?  23.  Mention  some 
which  are  not  boulders.  24.  How  can  you  tell  a  boulder  from 
any  other  loose  stone  ?  25.  What  is  a  ledge  of  rocks  ?  26. 
What  parts  of  our  country  are  destitute  of  boulders  ?  27.  Men- 
tion some  uses  for  boulders.  28.  What  is  the  weight  of  the 
great  Gilsum  boulder  in  N.  H.  ?  29.  Can  you  mention  any  other 
boulders  of  enormous  size  ?  30.  What  parts  of  our  country  are 
well  supplied  with  boulders?  31.  Explain  how  to  assort  the 
materials  in  the  soil.  32.  What  is  the  soil  principally  composed 
of  ?  33.  What  is  mud  ?  34.  Can  you  make  mud  out  of  stones? 
35.  If  so,  how  would  this  mud  differ  from  garden  soil  ? 

III. 

1.  Where  can  we  probably  find  a  bank  or  bed  of  gravel  ?  2. 
What  uses  are  made  of  gravel?  3.  What  uses  are  made  of 
sand  ?  4.  Are  gravel  and  sand  mostly  deep  in  the  earth  or  near 


204  GEOLOGICAL  EXCURSIONS. 

the  surface?  5.  What  different  kinds  of  materials  may  we 
probably  find  in  a  gravel  bank  ?  6.  What  is  sub-soil  ?  7.  Are 
the  different  parts  of  a  gravel  bank  stratified  or  unstratified  ?  8. 
What  is  meant  by  stratified  ?  9.  Are  any  parts  of  a  gravel  bank 
perfectly  stratified  ?  10.  What  are  laminae?  11.  When  is  a  bed 
of  sand  said  to  be  laminated?  12.  What  makes  stratification 
visible  in  a  sand  bank?  13.  What  is  a  talus?  14.  What  is 
the  origin  of  the  cobble  stones  along  the  foot  of  a  gravel  bluff  ? 

15.  What  is  it  which  sometimes  cements  gravel  stones  together  ? 

16.  What  is  the  color  of  the  iron  cement  ?     17.  How  deep  do  we 
sometimes   find   the   Drift   materials  ?       18.    Can  the   bed-rock 
always  be  found  at  some  depth  ?     19.    Is  the  Drift  always  par- 
tially stratified  throughout  its  entire  depth  ?     20.    Is  any  part  of 
the  Drift  ever  quite  unstratified  ?      21.    Which  is  uppermost,  the 
stratified  or  the  unstratified  Drift  ?     22.    Correct  this  sentence: 
"  The  well-digger  came  to  a  strata  of  clay."     23.    How  is  a  bed 
of  coarse  pebbles  produced  ?     24.    Mention  some  places  where 
coarse  pebbles  abound.      25.    Have  these  pebbles  been  thrown 
upon  the  beach  or  washed  out  of  the  bank  ?     26.    Did  you  ever 
find  a  bed  of  pebbles  cemented  into  a  solid  mass  ?      27.    Would 
such  a  mass  in  the  midst  of  the  Drift  be  still  a  part  of  the  Drift  ? 
28.    Is  the  Drift  always  composed  of  incoherent  materials  ?      29. 
How  are  sandy  capes  formed  ?     30.    What  are  sand  dunes  ?     31. 
Name  some  regions  noted  for  sand  dunes.     32.    Have  you  ever 
seen  the  sand  drifting  like  snow  before  the  wind  ? 

IV. 

1.  Do  any  water  currents  exist  beneath  the  surface  of  the 
earth  ?  2.  What  is  the  evidence  of  this  ?  3.  What  prevents 
the  underground  stream  from  soaking  into  the  earth  ?  4.  How 
are  underground  water  basins  formed  ?  5.  Suppose  no  clay  beds 
existed  in  the  Drift,  how  deep  would  the  water  sink  ?  6.  How 
deep  should  we  then  have  to  dig  to  obtain  wells?  7.  Where 
does  the  water  of  the  river  come  from  ?  8.  What  would  become 
of  the  river  if  there  were  no  clay  beds  for  it  to  flow  over  ?  9. 


QUESTION'S   OK   THE   TEXT.  205 

Did  you  ever  hear  of  rivers  which  soaked  into  the  underlying 
sand  and  disappeared  ?  10.  What  makes  a  sandy  desert  so  dry 
and  unproductive  ?  11.  In  digging  a  well,  what  kind  of  a 
stratum  must  be  reached?  12.  What  kind  of  a  stratum  is  water 
always  found  in?  13.  Suppose  you  find  water  above  a  clay 
stratum  and  then  make  a  hole  through  the  clay,  what  will  become 
of  the  water  ?  14.  Explain  how  two  wells  very  near  each  other 
may  be  of  very  different  depths.  15.  Explain  how  a  well  on  a 
hill  may  be  shallower  than  one  at  the  foot  of  the  hill.  16.  What 
is  meant  by  a  solution  of  limestone  ?  17.  Name  some  substances 
which  may  be  found  dissolved  in  spring  or  well  water  ?  18.  Why 
does  spring  water  often  deposit  something  ?  19.  How  is  traver- 
tin formed  ?  20.  How  is  calcareous  tufa  formed  ?  21.  What 
is  so-called  "  petrified  moss "  ?  22.  How  is  marl  formed  ?  23. 
What  is  shell  marl  ?  24.  What  makes  certain  waters  hard  ?  25. 
Name  some  part  of  the  country  where  the  waters  are  sometimes 
soft.  26.  What  is  a  chalybeate  spring  ?  27.  What  substance 
do  chalybeate  waters  deposit  ?  28.  What  is  its  usual  color  ?  29. 
What  other  substance  is  often  deposited  with  iron  oxide  ?  30.  Is 
the  deposit  of  iron  oxide  ever  sufficiently  abundant  to  have  any 
value  ?  31.  What  is  made  of  it  ?  32.  What  is  yellow  ochre  ? 
33.  What  is  the  rusty  cement  which  sometimes  holds  pebbles 
together?  34.  Mention  a  locality  where  rusted  pebbles  are 
plentiful  ? 

V. 

1.  Of  what  are  rocks  composed?  2.  Of  what  are  minerals 
composed  ?  3.  What  is  a  chemical  element  ?  4.  What  experi- 
ment may  be  performed  with  chalk  and  vinegar?  5.  What  other 
substances  might  be  used  to  produce  the  same  effect  ?  6.  What 
experiments  might  be  performed  with  limewater?  7.  What  is 
the  substance  which  clouds  the  limewater?  8.  What  acid  is  in 
it  ?  9.  Where  did  this  acid  come  from  ?  10.  What  is  a  chemical 
precipitate?  11.  When  the  fine  mud  from  the  soil  settled  in  our 
glass  vessel  (Figure  4)  was  that  a  chemical  precipitate  ?  12.  What 
are  atoms  ?  13.  What  substances  are  composed  of  atoms  ?  14. 


206  GEOLOGICAL  EXCURSIONS. 

Give  an  illustration  to  show  the  minuteness  of  atoms.  15.  How 
many  different  kinds  of  atoms  are  known  ?  16.  What  is  chemi- 
cal affinity  ?  17.  What  is  a  chemical  compound  ?  18.  Name 
some  substances  which  contain  only  one  chemical  element.  19. 
Name  some  which  contain  more  than  one  chemical  element.  20. 
Where  may  all  the  chemical  elements  be  found  ?  21.  Which  is 
the  most  abundant  of  the  elements?  22.  Which  are  the  three 
next  most  abundant  ?  23.  Name  the  other  elements  which  make 
an  important  part  of  the  earth.  24.  What  elements  exist  abun- 
dantly in  the  atmosphere  and  water  ?  25.  Which  element  has  an 
affinity  for  the  greatest  number  of  other  elements  ?  26.  What  is 
an  oxide  ?  27.  What  is  a  chloride  ?  28.  Name  an  oxide  and  a 
chloride.  29.  What  is  an  acid-forming  oxide  ?  30.  How  is  it 
converted  into  an  acid?  31.  What  is  a  basic  oxide  ?  32.  Name 
some  acids  and  bases.  33.  How  are  acids  and  bases  disposed 
toward  each  other?  34.  What  is  the  termination  of  the  name 
of  a  strong  acid?  35.  What  are  salts?  36.  When  does  the 
name  of  a  salt  end  in  ate?  37.  Can  carbonic  acid  remain  in 
combination  with  lime  when  sulphuric  acid  is  present  ?  38.  Why 
is  this?  39.  What  appearance  is  presented  when  the  carbonic 
acid  is  driven  off  ?  40.  Where  does  it  go  ?  41.  After  the  lime- 
water  in  the  bottle  is  covered  with  a  white  crust,  suppose  we  pour 
on  a  little  dilute  acid,  what  happens  to  the  crust  ?  42.  If  sul- 
phuric acid  was  poured  on,  what  new  substance  was  formed  ?  43. 
Where  is  it  ?  44.  What  is  precipitated  chalk  ? 

VI. 

1.  What  is  the  need  of  a  hammer  in  studying  geology?  2. 
Describe  a  suitable  style  of  hammer.  3.  How  do  we  determine 
the  hardness  of  minerals?  4.  What  is  the  hardest  mineral 
likely  to  be  found  ?  5.  Is  it  very  abundant  or  somewhat  rare  ? 
6.  What  different  colors  may  quartz  present  ?  7.  What  is  the 
color  of  pure  quartz  ?  8.  What  lustre  has  quartz  ?  9.  What  is 
flint  ?  10.  What  is  red  jasper  ?  11.  What  causes  the  colors  of 
the  different  varieties  of  quartz?  12.  What  gems  are  nothing 


QUESTIONS   ON   THE  TEXT.  207 

but  quartz?  13.  Of  what  chemical  substance  is  quartz  com- 
posed? 14.  How  many  elements  in  this  substance  ?  15.  What 
is  the  color  of  quartz  when  pure  ?  16.  What  is  its  crystalline 
form  ?  17.  What  proportion  of  ordinary  sand  is  composed  of 
quartz  ?  18.  To  what  uses  may  ordinary  sand  be  applied  ?  19. 
What  varieties  of  quartz  have  you  in  your  collection  ? 

VII. 

1.  What  can  you  say  of  the  abundance  of  quartz  ?  2.  How 
many  pounds  in  every  hundred  of  ordinary  rocks  are  quartz  ?  3. 
How  does  the  hardness  of  feldspar  compare  with  that  of  quartz  ? 
4.  How  does  its  lustre  compare  ?  5.  How  does  its  crystalline 
form  differ?  6.  Can  you  distinguish  any  flat,  crystalline  faces 
in  fragments  of  feldspar  ?  7.  Do  they  look  like  the  rough  frac- 
tures of  quartz  ?  8.  What  angle  do  they  sometimes  make  with 
each  other?  9.  Do  you  mean  that  all  the  angles  of  feldspar  are 
right  angles  ?  10.  Are  there  any  right  angles  in  a  crystal  of 
quartz?  11.  What  is  the  commonest  color  of  feldspar?  12. 
What  other  color  does  it  present?  J3.  Is  feldspar  ever  glassy 
like  quartz  ?  14.  How  does  the  crystalline  form  of  a  glassy 
feldspar  differ  from  quartz  ?  15.  What  peculiar  markings  on 
the  surface  of  some  feldspars?  16.  Is  the  common  feldspar  so 
striated?  17.  What  three  substances  in  the  composition  of  a 
feldspar?  18.  What  are  the  elements  in  each  of  these  sub- 
stances ?  19.  What  is  silicate  of  alumina  composed  of  ?  20.  If 
silicic  acid,  alumina  and  an  alkali  combine,  what  is  the  chemical 
name  of  the  compound  ?  21.  What  mineral  does  it  form  ?  22. 
Mention  several  alkaline  substances.  23.  Which  of  these  is  the 
alkali  in  common  feldspar?  24.  What  other  feldspars  are  there  ? 
25.  What  is  the  prevailing  color  of  soda-feldspar  ?  26.  What  is 
the  composition  of  a  glassy  feldspar?  27.  What  feldspar  is 
most  apt  to  be  dark-colored  ?  28.  What  is  the  name  of  common 
feldspar  ?  29.  What  name  is  applied  in  common  to  all  the  other 
feldspars  mentioned  ?  30.  What  causes  the  colors  of  the  feld- 
spars mentioned  ?  31.  In  100  pounds  of  orthoclase,  how  many 


208  GEOLOGICAL   EXCURSIONS. 

pounds  of  silica  ?  32.  How  many  pounds  of  each  of  the  other 
constituents  ?  33.  Of  what  is  common  clay  chiefly  composed  ? 
34.  What  is  kaolin  ?  35.  What  are  some  uses  of  feldspar  ?  36. 
In  what  kind  of  rocks  do  feldspars  occur  most  abundantly?  37. 
What  are  the  best  states  for  the  collection  of  feldspars?  38. 
What  states  do  not  contain  rocks  with  crystalline  feldspars? 
39.  Do  you  mean  that  none  of  these  states  have  boulders  con- 
taining feldspars?  40.  Were  your  specimens  of  feldspar  ob- 
tained from  boulders  or  from  rocks  in  place  ? 

VIII. 

1.  What  is  the  third  light-colored  mineral  studied  ?  2,  How 
does  calcite  compare  in  hardness  with  quartz  ?  3.  How  with 
feldspar  ?  4.  Can  you  often  find  calcite  in  boulders  ?  5.  Is 
calcite  as  glassy  as  quartz  ?  6.  Has  calcite  any  smooth  faces 
like  feldspar?  7.  How  then  can  you  distinguish  it  from  feld- 
spar ?  8.  Do  you  find  any  right  angles  in  calcite  ?  9.  How  do 
the  angles  of  calcite  differ  from  those  of  feldspar  ?  10.  What 
are  cleavage  lines?  11.  Is  calcite  ever  transparent  like  quartz? 
12.  How,  then,  can  you  distinguish  it  from  quartz  ?  13.  What 
is  the  name  of  a  common  variety  of  calcite  ?  14.  What  is  the 
crystalline  form  of  dog-tooth  spar?  15.  What  is  the  chemical 
name  of  calcite?  16.  How  does  it  compare  in  composition 
with  chalk  ?  17.  How  many  grains  of  carbonic  acid  in  100 
grains  of  calcite?  18.  How  many  grains  of  lime?  19.  What 
is  the  chemical  composition  of  carbonic  acid?  20.  What,  of 
lime  ?  21.  Represent  these  compounds  with  your  chemical 
cards.  22.  What  are  the  different  elements  present  in  carbon- 
ate of  lime  ?  23.  If  magnesia  is  put  in  place  of  lime,  what  does 
the  mineral  become  ?  24.  If  magnesia  is  added  to  the  lime, 
what  does  it  become?  25.  What  is  magnesite?  26.  What  is 
dolomite  ?  27.  Now,  what  are  the  chief  means  for  distinguish- 
ing calcite  from  quartz  and  feldspar?  28.  Which  of  these  will 
effervesce  with  acids?  29.  Which  is  hardest?  30.  Which 
softest?  31.  Which  most  pearly?  32.  Which  most  glassy? 


QUESTIONS   OK   THE   TEXT.  209 

33.  Which  has  right  angles  ?     34.  Which  sometimes  has  striated 
faces  ? 

IX. 

1.  What  is  the  prevailing  color  of  common  mica  ?  2.  Under 
what  form  does  it  exist  ?  3.  What  is  mica  sometimes  ignorant- 
ly  called?  4.  Are  the  leaves  of  mica  elastic  or  inelastic?  5. 
How  are  they  in  some  lustreless  conditions  of  mica  ?  6.  What 
is  the  degree  of  hardness  of  mica  ?  7.  What  are  the  colors  of 
mica  ?  8.  Where  may  large  plates  of  mica  be  obtained  ?  9. 
What  is  meant  by  saying  that  mica  is  the  name  of  a  family  of 
minerals?  10.  What  constituents  are  present  in  all  micas ?  11. 
What  are  the  chemical  elements  in  each  of  these  constituents  ? 
12.  What  is  the  name  of  common  mica  ?  13.  What  renders  it 
generally  dark-colored  ?  14.  What  constituent  causes  the  dull 
lustre  of  some  micas?  15.  What  are  such  micas  called?  16. 
What  other  dark  mineral  can  you  name?  17.  What  is  the 
color  of  hornblende?  18.  Is  this  a  common  or  a  scarce  min- 
eral? 19.  What  is  its  hardness?  20.  What  crystalline  form 
does  it  have  ?  21.  Is  this  form  like  quartz  ?  22.  When  lamel- 
lar, how  is  it  known  from  mica  ?  23.  Can  you  see  the  crystal- 
line form  of  hornblende  in  a  rock  ?  24.  What  chemical  con- 
stituents in  hornblende?  25.  What  colors  do  the  varieties  of 
hornblende  present?  26.  What  other  mineral  similar  to  horn- 
blende? 27.  What  color  does  augite  incline  to?  28.  What 
other  mineral  occurs  in  thin  scales?  29.  How  distinguished 
from  mica  ?  30.  What  are  the  prevailing  colors  of  talc  ?  31. 
What  is  its  composition?  32.  What  is  the  feel  of  talc?  33. 
What  is  soapstone  ?  34.  What  are  some  uses  of  soapstone  ? 

X. 

1.  Of  what  are  rocks  generally  composed?  2.  Of  what 
minerals  are  most  of  the  rocks  formed?  3.  How  can  we  have  so 
many  rocks  formed  from  so  few  minerals  ?  4.  Of  what  is  quartzite 
composed  ?  5.  Is  it  as  hard  as  quartz  ?  6.  What  is  a  common 


210  GEOLOGICAL   EXCURSIONS. 

color  for  quartzite?  7.  What  is  a  common  name  for  quartz 
boulders  ?  8.  What  is  a  vitreous  quartzite  ?  9.  When  is  a 
quartzite  conglomeritic  ?  10.  What  is  a  jaspery  quartzite?  11. 
What  is  a  quartzose  conglomerate  ?  12.  What  is  a  granular 
quartzite  ?  13.  What  is  a  grit  ?  14.  What  is  a  sandstone  ? 
15.  Name  some  fine  sandstones  used  for  building.  16.  Have 
you  ever  seen  the  New  York  Brownstone?  17.  Where  does  it 
come  from  ?  18.  Have  you  ever  noticed  the  Ohio  Freestones  ? 
19.  Where  are  many  grindstones  obtained?  20.  What  differ- 
ent colors  does  the  Waverly  Sandstone  present  ?  21.  What 
impurities  are  sandstones  likely  to  contain  ?  22.  What  is  a 
micaceous  sandstone  ?  23.  How  many  kinds  of  quartzose  rocks 
can  you  now  name  ? 

XI. 

1.  Why  is  it  more  convenient  to  study  boulders  than  rocks 
in  ledges  ?  2.  Why,  otherwise,  is  it  better  to  do  so  ?  3.  What 
is  one  of  Nature's  methods  for  sticking  together  grains  of  sand  ? 
4.  How  can  you  ascertain  whether  a  rock  contains  calcium  car- 
bonate ?  5.  Are  all  rocks  stuck  together  with  calcium  carbon- 
ate ?  6.  What  mineral  has  great  fondness  for  the  company  of 
quartz  ?  7.  What  other  mineral  is  generally  found  in  company 
with  these  two  ?  8.  How  can  you  distinguish  feldspar  from 
calcite  ?  9.  What  is  the  composition  of  granite  ?  10.  Is  this 
rock  stratified  or  unstratified?  11.  What  is  the  coarseness  of 
granite  ?  12.  Which  is  most  valuable,  a  coarse  granite  or  a  fine 
one  ?  13.  What  is  a  porphyritic  granite  ?  14.  When  is  any 
rock  called  porphyritic  ?  15.  What  is  the  color  of  the  quartz  in 
granite?  16.  What,  of  the  feldspar?  17.  What,  the  mica? 
18.  What  makes  the  reddish  spots  in  granite  ?  19.  How  many 
kinds  of  quartz  in  granite?  20.  How  many  of  feldspar?  21. 
How  many  of  mica  ?  22.  How  much  mica  in  granite  ?  23.  What 
gives  granite  sometimes  a  dark  complexion  ?  24.  What  gives  it 
a  reddish  complexion  ?  25.  When  does  granite  have  a  grayish 
hue?  26.  What  is  a  granulite?  27.  What  is  a  felsite  ?  28. 
What  is  a  petrosilex ?  29.  What  are  the  uses  of  granite?  30. 


QUESTIONS   ON   THE  TEXT.  211 

What  is  a  mica  schist  ?  31.  Which  contains  most  feldspar, 
gneiss  or  mica  schist  ?  32.  What  is  a  hydromica  schist  ?  33. 
Are  schists  stratified  or  unstratified  ?  34.  How  can  you  tell  a 
mica  schist  from  a  gneiss?  35.  What  is  greisen?  36.  What 
must  be  added  to  greisen  to  make  it  granite  ?  37.  What  must 
be  added  to  a  granular  felsite  to  make  it  granite?  38.  What 
must  be  added  to  granulite  to  make  it  granite  ? 

XII. 

1.  What  uses  are  sometimes  made  of  boulders  ?  2.  What 
opportunity  is  furnished  the  geological  student  at  the  building 
of  a  boulder  house  ?  3.  What  colors  of  rocks  may  be  seen  at 
a  stone-cutter's  yard  ?  4.  What  is  the  general  appearance  of  a 
hornblendic  rock  ?  5.  What  minerals  are  apt  to  be  associated 
with  hornblende  ?  6.  What  is  syenite  composed  of  ?  7.  What 
is  the  origin  of  the  name  ?  8.  What  other  rock  does  syenite 
resemble  ?  9.  What  is  so  called  "  Scotch  Granite  "?  10.  What 
is  "  Quincy  Granite  "?  11.  Mention  some  buildings  constructed 
of  syenite.  12.  Where  may  syenite  be  found  besides  in  bould- 
ers ?  13.  How  does  syenite  compare  with  granite  in  durability  ? 
14.  What  is  a  micaceous  syenite  ?  15.  What  is  a  hornblendic 
granite?  16.  What  is  a  hyposyenite?  17.  What  is  diorite? 
18.  How  does  it  differ  from  hyposyenite?  19.  What  is  diabase? 
20.  What  is  a  plagioclase  feldspar?  21.  What  is  syenitic 
gneiss  ?  22.  Wh&t  is  dioritic  gneiss  ?  23.  What  is  diabasic 
gneiss?  24.  What  is  hornblende  schist?  25.  What  is  horn- 
blende rock?  26.  What  feldspar  is  dark- colored  ?  27.  When 
is  a  rock  said  to  be  phanerocrystalline  ?  28.  When  is  it  said  to 
be  cryptocrystalline  ?  29.  Define  "massive,"  "gneissoid"  and 
"  schistose."  30.  What  is  protogine  ?  31.  What  is  protogine 
gneiss  ?  32.  What  is  talcose  schist  ?  33.  What  is  talc  rock  ? 
34.  What  is  steatite  ?  35.  What  massive  rocks  contain  quartz  ? 
36.  What  ones  contain  no  quartz  ?  37.  What  rocks  contain 
hornblende  ?  38.  What  must  be  added  to  greisen  to  make  gran- 
ite ?  39.  What  to  hyposyenite  to  make  syenite  ? 


212  GEOLOGICAL  EXCURSIONS. 

XIII. 

1.  When  is  a  rock  said  to  be  calciferous  ?  2.  What  is  a  cal- 
careous rock  ?  3.  What  degree  of  hardness  have  marbles  ?  4. 
What  is  the  effect  of  acid  on  them?  5.  What  is  a  dolomitic 
marble  ?  6.  How  may  it  be  made  to  effervesce  ?  7.  Of  what 
mineral  are  marbles  composed?  8.  Are  the  separate  crystals 
visible  ?  9.  What  is  saccharoidal  marble  ?  10.  What  is  statuary 
marble?  11.  Mention  different  varieties  of  marbles.  12.  What 
causes  reddish  colors  in  marbles?  13.  What  blackish  colors? 
14.  What  bluish  colors?  15.  What  is  a  pudding-stone  marble? 
16.  What  is  a  shell  marble?  17.  State  where  different  kinds  of 
marbles  are  quarried.  18.  What  is  common  limestone  ?  19. 
How  does  its  composition  compare  with  that  of  marble  ?  20. 
How  does  its  stratification  compare  with  that  of  marble  ?  21.  In 
what  three  ways  may  limestones  be  distinguished  from  most 
other  rocks  ?  22.  What  is  ob'litic  limestone  ?  23.  How  are  the 
following  words  used:  silicious,  argillaceous,  arenaceous,  ferru- 
ginous, carbonaceous,  bituminous,  petroliferous  ?  24.  What 
distinction  may  be  made  between  argillaceous  and  aluminous  ? 
25.  How  does  chalk  differ  from  common  limestone  ?  26.  Where 
does  marl  originate  ?  27.  What  is  it  ?  28.  What  is  travertin  ? 
29.  What  is  calcareous  tufa?  30.  What  is  a  stalactite?  31. 
What  is  stalagmite  ?  32.  How  does  it  compare  with  travertin  ? 
33.  Which  is  the  most  durable  material,  marble  or  granite  ? 

XIV. 

1.  What  is  graphic  slate?  2.  How  does  the  hardness  of 
slate  compare  with  that  of  quartzite?  3.  Why  does  slate  not 
effervesce  with  acid  ?  4.  What  does  slate  become  when  pulver- 
ized and  moistened  ?  5.  Of  what  are  bricks  made  ?  6.  Is  there 
any  fine  sand  in  clay  ?  7.  How  may  it  be  separated  ?  8.  What 
is  the  characteristic  substance  in  clay  ?  9.  When  is  a  substance 
said  to  be  aluminous  ?  10.  What  is  the  difference  between  slate 
and  shale  ?  11.  What  is  argillite  ?  12.  How  does  it  compare  in 
hardness  with  shale  and  slate  ?  13.  Of  what  is  argillite  com- 


QUESTIONS   ON   THE  TEXT. 

posed  ?  14.  What  is  kaolin  ?  15.  From  what  is  kaolin  formed  ? 
16.  What  has  become  of  the  alkali  in  the  feldspar  ?  17.  What 
is  the  use  of  kaolin  ?  18.  What  effect  has  remaining  alkali  upon 
the  porcelain?  19.  What  is  sometimes  used  in  porcelain-making 
besides  kaolin?  20.  What  is  the  cause  of  the  red  color  of 
bricks?  21.  What  are  the  groups  of  fragmental  rocks?  22. 
What  are  the  four  conditions  in  which  fragmental  rocks  exist  ? 
23.  Name  some  indurated  silicious  rocks.  24.  Name  some  in- 
durated calcareous  rocks.  25.  Name  an  incoherent  calcareous 
rock.  26.  Name  a  crystalline  calcareous  rock.  27.  Which  is 
the  commonest  class  of  bed  rocks?  28.  What  class  of  rocks 
furnishes  the  greatest  number  of  species  and  varieties  ?  29.  In 
what  parts  of  our  country  are  the  bed  rocks  mostly  fragmental  ? 
30.  Where  are  they  mostly  crystalline  ?  31.  What  is  a  mica- 
ceous slate  ?  32.  What  is  a  calcareous  sandstone  ? 

XV. 

1.  What  are  the  two  principal  divisions  of  crystalline  rocks  ? 

2.  What  are  the   two   divisions   of    phanero-crystalline   rocks  ? 

3.  Which  division  embraces  the  greatest   number   of    species? 

4.  What  is  the  only  phanero-crystalline  rock  which  effervesces 
with  acids  ?     5.    If  a  rock  is  composed  wholly  of  quartz,  what  is 
its  name  ?     6.    What,  if   of   quartz  and  feldspar  in   crystalline 
grains  ?     7.  What,  if  composed  of  quartz  and  mica  ?     8.  What, 
if  of  quartz,  feldspar  and  mica  ?     9.  What  rock  is  made  from  the 
union  of  hydromica  and  quartz  ?     10.    Hornblende  and  quartz  ? 
11.    Hornblende  and  orthoclase  ?      12.    Hornblende   and  plagio- 
clase?     13.    Augite  and  quartz?     14.    Augite  and  plagioclase  ? 
15.    Talc   and    quartz?     16.    Talc,   quartz   and    orthoclase?     17. 
Talc  alone?     18.    Hornblende    alone?     19.    Augite  alone?     20. 
What  are  some  cryptocrystalline  rocks  ?     21.    What  is  felsite  ? 
22.  What  is  aphanite  ?     23.  What  is  hyposyenite  ?     24.  What  is 
diorite  ?     25.    How  does  diorite  differ  from  diabase  ?     26.   How 
does  felsite  differ  from  granulite  ? 


214  GEOLOGICAL  EXCURSIONS. 

XVI. 

1.  How  does  water  assort  the  materials  which  it  moves  ?  2. 
Would  any  assortment  take  place  if  all  the  water  continued  to 
have  the  same  motion  ?  3.  When  a  torrent  flows  down  a  slope, 
where  are  the  coarser  materials  deposited  ?  4.  Where  are  the 
finer  deposited  ?  5.  What  is  alluvium  ?  6.  What  is  the  origin 
of  the  shells  found  in  some  alluvium  ?  7.  In  what  kind  of  water 
do  flags  and  rushes  grow  ?  8.  On  which  side  of  a  pond  may 
we  find  them?  9.  What  is  the  origin  of  peat?  10.  What 
caused  the  marsh  and  meadow  flat  upon  the  border  of  the  pond  ? 
11.  Is  there  any  danger  that  the  pond  may  become  completely 
filled  ?  12.  What  would  be  in  its  place  after  that  ?  13.  Why 
does  the  peat  form  on  one  side  of  the  pond,  and  not  on  all  sides  ? 

14.  What  is  the  prevailing  direction  of  the  wind  in  our  region? 

15.  Then  on  which  side  of  the  pond  should  the  peat  marsh  be  ? 

16.  What  is  contributed  to  the  pond  from  the  surrounding  hill 
slopes?     17.    How  is  the  matter  transferred  to  the  pond?     18. 
Where  are  the  coarse  portions  of  it  deposited  ?     19.    Have  you 
ever  seen  a  spot  where  there  was  once  a  lakelet  which  has  been 
filled?     20.    What  are  bivalves  and  univalves?     21.    Where  do 
they  get  the  material  for  their  shells?     22.    What  becomes  of 
the   shells  when   the  animals  die?     23.    What   is  the  origin  of 
rnarl  ?      24.    Where   does  the  mud  in  the   stream   come  from  ? 
25.  Where  is  it  going  ?     26.    How  does  the  sediment  get  in  the 
sea  ?     27.    How   does  the  Mississippi  become  so   muddy  ?     28. 
What   does  it   do  with  its  mud?     29.   What  is  the  bar  of  the 
Mississippi?     30.    Do  other  rivers  also  have  bars?     31.  What  is 
a  river  delta?     32.  What  becomes  of  the  sediment  carried  far 
beyond  the  mouth  of  a  river  ?     33.  What  is  river  sediment  form- 
ing in  the  bottom  of   the  ocean?     34.  What  effects  do  ocean 
waves  produce  upon  the   shores?     35.    What  becomes  of    the 
material  of  the  crumbling  shore  ? 


QUESTIONS   ON   THE   TEXT.  215 

XVII. 

1.  What  is  the  source  of  the  sediment  in  the  roadside  stream  ? 
2.  What  is  erosion  ?  3.  How  has  the  ravine  been  produced  ?  4. 
Why  is  the  bed  of  the  brook  so  stony  ?  5.  Where  have  the 
sand  and  loam  gone  ?  6.  By  what  means  does  the  stream  widen 
its  valley  ?  7.  How  do  we  know  its  valley  was  once  narrower  ? 
8.  Mention  a  fine  example  of  a  rock-worn  gorge.  9.  Where  has 
the  sediment  gone  from  Watkins'  Glen  ?  10.  Mention  a  fine 
case  of  river  erosion  in  Wisconsin.  11.  What  great  river  has 
performed  a  vast  amount  of  erosion  ?  12.  In  what  states  may 
examples  of  it  be  seen  ?  13.  What  river  in  the  Far  West  has 
worn  very  deep  gorges  ?  14.  Where,  besides  in  the  river  gorges, 
are  the  rocks  wearing  away  ?  15.  By  what  means  are  the  rocks 
everywhere  destroyed  ?  16.  Where  may  be  seen  a  great  thick- 
ness of  decayed  rocks  ?  17.  What  is  the  evidence  that  the  rocks 
are  decayed  ?  18.  Have  the  rocks  decayed  similarly  in  the 
Northern  States  ?  19.  What  has  become  of  the  decayed  material  ? 
20.  How  may  a  natural  bridge  be  caused?  21.  What  grand 
examples  of  erosion  may  be  seen  in  Tennessee  ?  22.  What  is 
the  basin  of  middle  Tennessee  ?  23.  What  is  the  valley  of  east 
Tennessee  ?  24.  What  enormous  example  of  erosion  may  be 
mentioned  in  Pennsylvania?  25.  How  high  a  mountain  has 
been  worn  down  ?  26.  In  what  part  of  Pennsylvania  may  this 
result  be  seen  ?  27.  How  do  we  know  such  a  mountain  was  ever 
there  ?  28.  How  do  rock  columns  come  into  existence  ?  29. 
Where  may  rock  columns  be  seen? 

XVIII. 

1.  How  would  the  sea  sediments  appear  if  we  could  bring  up 
an  acre  and  inspect  them  ?  2.  How  would  the  different  layers  be 
distinguished  ?  3.  What  relics  would  they  contain  ?  4.  On 
what  would  the  depth  of  the  sediments  depend  ?  5.  Where  could 
you  say  the  sediments  came  from  ?  6.  How  might  the  sea  sedi- 
ments be  converted  to  rock  ?  7.  What  would  make  the  rock  a 
stratified  one  ?  8.  What  would  be  the  laminae  in  the  rock  ?  9. 


216  GEOLOGICAL   EXCURSIONS. 

What  would  make  fossils  in  the  rock  ?  10.  Are  there  really  any 
rocks  such  as  these  sea  sediments  would  be  under  the  circum- 
stances stated  ?  11.  What  rocks  are  they  ?  12.  What  besides 
sediments  do  limestones  contain  ?  13.  In  what  parts  of  the 
country  are  the  rocks  mostly  crystalline?  14.  In  what 
parts  are  they  mostly  uncrystalline  ?  15.  Which  kind 
contain  most  fossils  ?  16.  From  which  kind  are  most  of  the 
boulders  derived  ?  17.  Which  kind  are  uppermost  ?  18.  How  is 
their  age  indicated  by  their  relative  position  ?  19.  What  is 
metamorphism  ?  20.  What  three  kinds  of  action  had  much  to 
do  with  metamorphism  ?  21.  What  is  the  position  of  the  older 
rocks  ?  22.  How  do  the  fossils  differ  among  the  uncrystalline 
rocks.  23.  Which  existed  first,  marine  animals,  or  terrestrial  ? 

24.  State  the  order  of  appearance  of  different  types  of  animals. 

25.  What  are  said  to  be  some  of  the  most  important  facts  in 
geology  ?     26.    Give  the   names  of   the  Great  Systems  in  their 
order.      27.    Give  the  names  of  the  Systems  in  their  order.      28. 
Now  recite   them    in   the    opposite    order.     29.  What    Systems 
belong  to   the   Mesozoic?     30.    What   to   the   Palaeozoic  ?     31. 
What  to  the  Eozoic  ? 

XIX. 

1.  How  can  you  illustrate  the  systems  of  strata  with  an 
onion  ?  2.  Is  this  a  good  illustration  ?  3.  In  what  respect  is  it 
incorrect  ?  4.  Are  Caenozoic  rocks  everywhere  at  the  surface  ? 
5.  Are  Mesozoic  rocks  always  the  next  under  Caenozoic?  6. 
What  system  of  rocks  may  be  found  at  the  surface  ?  7.  Is  the 
earth's  surface  completely  undistorted  ?  8.  What  does  Figure 
31  represent  ?  9.  In  what  respect  is  this  figure  incorrect  ?  10. 
Why  is  nothing  represented  in  the  interior?  11.  What  is  the 
earth's  crust  ?  12.  When  is  one  formation  said  to  overlie 
another  ?  13.  What  is  the  dip  of  a  formation  ?  14.  When  is  a 
rock  said  to  outcrop  ?  15.  What  system  of  rocks  completely 
surrounds  the  earth  ?  16.  Is  this  system  everywhere  covered  by 
later  formations  ?  17.  Is  it  anywhere  covered  by  all  the  later 
formations  ?  18.  Which  system  of  rocks  has  least  extent  on  the 


QUESTIONS   ON   THE   TEXT.  217 

earth's  surface  ?  19.  Why  do  not  Mesozoic  and  Palaeozoic  strata 
cover  all  the  earth  ?  20.  Why  do  they  not  have  as  great  an 
extent  as  formerly  ?  21.  Is  it  to  be  supposed  they  ever  covered 
the  whole  earth  like  the  Eozoic  ?  22.  What  were  the  Caenozoic 
rocks  formed  from  ?  23.  How  is  it  that  some  portions  of  the 
Eozoic  rocks  are  now  above  sea  level  ?  24.  How  are  they  higher 
than  some  Mesozoic  and  Caenozoic  strata  ?  25.  Explain  how  to 
make  a  little  map  of  the  region  about  d  near  the  lower  side  of 
Figure  31.  26.  Please  make  a  map  of  the  region  about  G,  Fig- 
ure 31.  27.  What  is  the  difference  in  the  dip  of  the  strata  in 
these  two  maps  ?  28.  Which  way  do  rocks  always  dip  in  respect 
to  newer  and  older  strata  ? 

XX. 

I.  What  is  shown  by  a  geological  map?  2.  In  what  part  of 
the  United  States  are  the  newer  rocks  ?  3.  In  what  part  are  the 
older  rocks  ?  4.  What  are  the  principal  Eozoic  areas  shown  on 
our  geological  map  ?  5.  What  system  of  strata  is  generally  seen 
next  to  Eozoic  rocks  ?  6.  What  is  the  law  of  the  dip  of  strata  ? 
7.  If  Devonian  rocks  pass  under  Coal  Measures,  may  the  same 
Devonian  rise  anywhere  to  a  greater  height  than  the  Coal  Meas- 
ures ?  8.  Explain  how  this  can  be.  9.  Draw  a  diagram  illus- 
trating it.  10.  What  systems  belong  between  the  Cambrian  and 
the  Lower  Carboniferous?  11.  Now  look  at  the  Cambrian 
region  in  Tennessee  along  its  eastern  border;  what  system  of 
rocks  joins  it  ?  12.  Why  are  there  no  Silurian  and  Devonian  ? 
13.  Can  you  find  any  Jura-Trias  in  Connecticut  ?  14.  What 
system  of  rocks  does  it  rest  on  ?  15.  What  systems  are  wanting 
between  the  two  ?  16.  Why  are  they  not  there  ?  17.  Where  is 
the  most  elevated  region  in  Wisconsin  ?  18.  On  the  line  from 
that  region  to  Chicago,  which  way  do  the  rocks  dip  ?  19.  If 
there  is  a  sandstone  at  the  bottom  of  the  Cambrian,  would  that 
be  found  under  Chicago  ?  20.  Would  the  outcrop  of  that  sand- 
stone in  Wisconsin  be  higher  or  lower  than  the  surface  at  Chi- 
cago? 21.  If  rain  should  fall  on  that  elevated  Wisconsin 
outcrop,  how  far  would  it  flow  through  the  sandstone  ?  22.  Do 


218  GEOLOGICAL   EXCURSIONS. 

you  imagine  it  would  ever  get  as  far  as  under  Chicago  ?  23. 
Then  if  you  should  bore  down  at  Chicago,  into  that  sandstone, 
what  would  rise  out  from  the  hole  ?  24.  Would  this  be  an 
artesian  well  ?  25.  Now  please  make  a  drawing  explaining  it 
all. 

XXI. 

1.  What  is  a  geological  map?  2.  Does  a  geological  map 
teach  anything  more  than  what  appears  on  the  surface  of  the 
earth?  3.  What  must  we  attempt  to  do  in  studying  such  a 
map  ?  4.  What  is  a  geological  section  ?  5.  In  constructing  a 
section  from  Detroit  to  Grand  Haven,  what  is  the  first  thing  to 
do  ?  6.  Is  it  necessary  to  lay  off  precisely  the  distances  shown 
on  the  map  ?  7.  Will  the  section  be  correct  if  we  take  any  mul- 
tiple of  the  map  distances  ?  8.  What  is  a  multiple  ?  9.  How 
do  we  know  in  what  direction  to  draw  the  lines  of  dip  from  the 
points  determined  ?  10.  Why  do  we  not  draw  lines  of  dip  down 
from  Detroit  and  from  Grand  Haven  ?  11.  Where,  on  the  west, 
is  the  boundary  between  the  Devonian  and  Silurian  ?  12.  What 
is  a  geological  profile  ?  13.  How,  from  the  study  of  a  common 
map,  can  we  get  an  idea  of  the  surface  configuration  of  a  region  ? 
14.  How  is  it  shown  that  the  centre  of  Michigan  is  somewhat 
elevated  ?  15.  What  right  have  we  to  represent  Cambrian  and 
Eozoic  in  a  section  from  Detroit  to  Grand  Haven  ?  16.  Explain 
how  to  construct  a  section  from  Canada  to  the  Coal  region  of 
Pennsylvania.  17.  What  may  we  infer  about  the  surface  con- 
figuration along  this  line  ?  18.  Why  do  we  generally  represent 
dips  steeper  than  they  really  are  ?  19.  What  effect  has  this  on 
the  apparent  thickness  of  the  formations  ?  20.  In  representing 
the  elevations  and  depressions  of  the  surface,  can  we  conveniently 
use  the  same  scale  as  in  the  distances  along  the  surface  ?  21. 
Explain  how  to  complete  the  section  when  the  surface  features 
are  to  be  shown.  22.  Construct  a  profile  section  from  St.  Louis, 
Missouri,  to  Columbus,  Ohio. 


QUESTIONS   ON   THE   TEXT.  219 

XXII. 

1.  Name  all  the  states  in  which  any  Eozoic  rocks  appear.  2. 
Name  all  in  which  none  appear.  3.  What  state  has  the  greatest 
area  of  Eozoic  rocks?  4.  What  areas  in  the  United  States  are 
connected  with  the  Canadian  Eozoic  ?  5.  By  what  means  may 
we  easily  become  acquainted  with  the  kinds  of  rocks  in  the 
Eozoic  ?  6.  What  New  England  mountains  are  mostly  composed 
of  Eozoic  rocks  ?  7.  Mention  some  separate  mountain  summits 
of  the  White  Mountain  chain.  8.  What  forms  does  weathering 
most  commonly  produce  in  granitic  and  gneissic  rocks  ?  9.  How 
are  pinnacled  mountains  produced  ?  10.  In  what  mountains  are 
such  summits  common?  11.  What  is  the  arrangement  of  the 
strata  in  Mt.  Kearsarge?  12.  What  evidences  are  shown  of 
extensive  weathering  ?  13.  What  is  the  appearance  of  a  section 
through  the  Canadian  Eozoic  ?  14.  Where  have  been  found  the 
remains  of  the  oldest  animals  that  ever  lived  on  the  earth?  15. 
What  is  the  appearance  of  a  section  through  the  Wisconsin 
Eozoic?  16.  Into  what  two  systems  is  the  Eozoic  divided ?  17. 
What  kinds  of  rocks  occur  in  the  Laurentian  ?  18.  What  occur 
in  the  Huronian  ?  19.  What  is  the  geological  position  of  the 
oldest  iron  ores?  20.  Does  the  Huronian  produce  iron?  21. 
Where  ?  22.  How  does  the  iron  occur  in  some  cases,  as,  for 
instance,  at  Marquette?  23.  How  does  it  occur  at  Pilot  Knob? 
24.  How  in  the  Penokie  Iron  Range  ?  25.  Point  out  some 
locality  where  the  Laurentian  and  Huronian  are  uncomformable. 
26.  What  overlies  the  Huronian  in  the  Penokie  Range  ?  27. 
What  useful  metal  is  afforded  by  the  Kewenian  rocks  ?  28.  How 
do  we  know  the  Eozoic  rocks  to  be  older  than  any  others  ?  29. 
What  is  the  thickness  of  the  Eozoic  rocks?  30.  What  indica- 
tions have  we  of  the  vast  age  of  the  world  ?  31.  What  do  Ages 
and  Eras  correspond  to?  32.  What  evidences  of  the  exertion  of 
immense  forces  are  revealed  in  the  Eozoic  rocks  ?  33.  What  is 
the  aim  of  the  science  of  geology  ? 


220  GEOLOGICAL  EXCURSIONS. 

XXIII. 

1.  What  northwestern  states  contain  Cambrian  rocks?  2. 
What  parts  of  Canada  contain  them  ?  3.  What  interior  states 
contain  them?  4.  What  sea-board  states?  5.  What  large 
cities  are  located  on  Cambrian  strata  ?  6.  In  what  respect 
do  Cambrian  strata  differ  from  Eozoic  ?  7.  How  are  the  bluffs 
of  the  upper  Mississippi  formed  ?  8.  What  has  caused  the  burial 
of  the  bases  of  those  bluffs  ?  9.  Explain  how  the  "  Hornet's 
Nest "  has  been  formed.  10.  How  has  "  Castle  Rock,"  in  Min- 
nesota, been  formed?  11.  What  is  meant  by  an  outlier?  12. 
What  is  the  name  of  the  lowest  sandstone  ?  13.  What  is  the 
formation  next  above  ?  14.  What  is  the  St.  Peter's  Sandstone  ? 
15.  On  what  formation  does  the  city  of  St.  Paul  stand  ?  16. 
What  produces  the  "  Falls  of  St.  Anthony  "  ?  17.  State  the  four 
formations  which  make  up  the  Cambrian  system  in  Wisconsin 
and  Minnesota.  18.  State  why  the  St.  Peter's  Sandstone  is  at 
the  river  level  at  Fort  Snelling,  and  not  so  at  McGregor.  19. 
Describe  the  condition  of  the  upper  surface  of  the  Eozoic  in 
Wisconsin.  20.  Is  extensive  erosion  shown  by  any  other  mem- 
ber of  the  Cambrian  system  ?  21.  What  do  these  eroded  surfaces 
indicate  ?  22.  What  great  changes  took  place  while  these  for- 
mations were  accumulating  ?  23.  Why  is  the  Potsdam  Sandstone 
in  Minnesota  of  such  varying  thickness  ?  24.  Describe  the  sec- 
tion in  Sauk  county,  Wisconsin.  25.  Explain  how  the  columns 
shown  have  been  caused.  26.  What  are  the  indications  of  a 
break  between  the  Eozoic  and  Cambrian  ?  27.  Describe  the 
Cambrian  strata  in  the  Cincinnati  region.  28.  Describe  the  dips 
about  Cincinnati.  29.  How  do  the  rocks  here  differ  from  the 
Wisconsin  Cambrian  ?  30.  What  three  groups,  in  general,  con- 
stitute the  Cambrian? 

XXIV. 

1.  What  is  the  depth  of  the  gorge  at  Niagara  Falls?  2. 
Which  way  do  the  formations  dip  along  the  Niagara  River  ?  3. 
Where  does  the  gorge  of  Niagara  terminate  on  the  north  ?  4. 


QUESTIONS   ON   THE   TEXT.  221 

What  is  the  upper  formation  of  the  Falls  ?  5.  In  which  direction 
does  the  Niagara  Limestone  grow  thinner  ?  6.  What  forms  the 
rapids  above  Niagara  Falls  ?  7.  What  may  be  seen  under  the 
Falls  ?  8.  How  is  space  made  there  for  standing  ?  9.  What 
causes  the  recession  of  the  Falls?  10.  How  rapidly  do  they 
recede?  11.  What  was  Table  Rock?  12.  What  formations 
may  be  traced  below  the  Niagara  Shale  ?  13.  What  ore  is  found 
in  the  Clinton  Group  ?  14.  Where  is  the  Medina  Sandstone  ? 
15.  What  is  its  appearance  ?  16.  What  are  its  uses  ?  17.  What 
group  next  above  the  Niagara  Group  ?  18.  Where  may  the 
Silurian  rocks  be  studied  ?  19.  Of  what  do  they  consist  ?  20. 
What  valuable  products  are  found  in  the  Salina?  21.  How  is 
brine  obtained  at  Syracuse  ?  22.  Is  any  rock  salt  found  in  the 
Salina  Group  ?  23.  At  what  places  ?  24.  What  new  salt  dis- 
trict has  recently  been  developed  ?  25.  Is  there  any  prospect  of 
getting  brine  by  boring  at  any  other  points  in  New  York  ?  26. 
What  change  do  the  Niagara  and  Salina  groups  undergo  when 
traced  eastward  ?  27.  What  group  above  the  Salina  ?  28. 
Where  is  it  extensively  developed  ?  29.  In  what  western  states 
is  the  Helderberg  known  ?  30.  In  what  eastern  states  ?  31.  In 
what  British  Provinces  ?  32.  Name  now  the  groups  which  make 
up  the  Silurian  system.  33.  Name  the  groups  of  the  Cambrian 
and  Silurian  from  below  upward.  34.  Name  them  from  above 
downward. 

XXV. 

1.  What  is  the  elevation  of  Mackinac  Island?  2.  Of  what 
rocks  composed  ?  3.  How  do  they  compare  with  the  rocks  on 
the  main  land  ?  4.  Through  what  formations  have  the  Straits 
been  excavated  ?  5.  By  what  agency  does  the  excavation  seem 
to  have  been  made  ?  6.  Describe  "  Sugar  Loaf  "  at  Mackinac. 
7.  Describe  "  Arched  Rock."  8.  What  is  the  name  of  this  lime- 
stone. 9.  To  what  region  westward  may  the  Devonian  be  traced  ? 
10.  What  is  the  age  of  the  rocks  at  Little  Traverse  Bay?  11. 
In  what  direction  from  Little  Traverse  Bay  are  Chemung  rocks 
to  be  found  ?  12.  What  is  their  character  in  Michigan  ?  13.  To 


222  GEOLOGICAL   EXCURSIONS. 

what  regions  may  the  Devonian  rocks  be  traced  eastward  ?  14. 
What  Canadian  cities  are  located  on  the  Corniferous  Limestone  ? 
15.  What  New  York  cities  are  on  the  Devonian  ?  16.  What  is 
the  geological  position  of  Syracuse?  17.  In  what  formation  is 
the  valley  of  Onondaga  Creek  excavated?  18.  What  is  the 
Oriskany  Sandstone  ?  19.  From  Syracuse,  which  way  must  we 
travel  to  find  newer  rocks  ?  20.  What  group  of  rocks  overlies 
the  Corniferous  ?  21.  What  overlies  the  Hamilton  ?  22.  Men- 
tion localities  of  the  Chemung.  23.  What  Ohio  cities  are  on  the 
Devonian  ?  24.  In  what  part  of  Ohio  are  the  Chemung  strata  ? 
25.  Recite  the  names  of  the  groups  of  Devonian  strata.  26. 
Enumerate  all  the  groups  from  the  top  of  the  Devonian  to  the 
bottom  of  the  Cambrian. 

XXVI. 

1.  What  is  the  height  of  the  bluff  at  Burlington,  Iowa?  2. 
What  kind  of  rocks  at  the  top  of  the  bluff  ?  3.  What  kind  of 
rocks  at  the  bottom  ?  4.  How  many  different  groups  are  found 
here  ?  5.  What  is  the  name  of  the  upper  group  ?  6.  What  the 
name  of  the  lower  group  ?  7.  How  do  we  know  it  is  proper  to 
divide  these  rocks  into  two  groups?  8.  What  interesting  fossils 
in  the  upper  group  ?  9.  What  kind  of  limestone  at  the  top  of 
the  lower  group  ?  10.  How  do  we  know  it  belongs  to  the  lower 
group  rather  than  the  upper  ?  11.  By  what  other  means  than 
the  fossils  may  two  groups  be  distinguished  ?  12.  Mention  a 
case  where  an  eroded  surface  separates  two  groups.  13.  Mention 
a  case  where  difference  of  dip  separates  two  groups.  14.  May 
two  groups  be  truly  distinct  without  any  appearance  of  uncon- 
formability  or  intervening  erosion  ?  15.  How  then,  can  we  know 
they  are  distinct?  16.  Suppose  there  are  no  fossils,  can  we  then 
prove  them  distinct  ?  17.  Point  out  regions  covered  by  Lower 
Carboniferous.  18.  In  what  formation  is  Mammoth  Cave  ?  19. 
How  was  the  cave  produced  ?  20.  What  is  the  knob  region  ? 
21.  How  are  its  features  caused  ?  22.  What  change  takes  place 
as  we  follow  the  Carboniferous  Limestone  into  Pennsylvania  ? 
23.  How  is  the  Lower  Carboniferous  located  in  Michigan  ?  24. 


QUESTIONS   ON   THE   TEXT.  223 

What  is  the  character  of  the  lower  part  of  the  Carboniferous 
Limestone  Group  in  Michigan  ?  26.  How  do  we  know  the 
gypsum  formation  is  a  part  of  that  group  ?  26.  What  other 
region  has  a  salt-and-gypsum  deposit  in  the  Lower  Carboniferous  ? 
27.  How  is  brine  obtained  along  the  Saginaw  Valley?  28.  Does 
this  brine  come  from  the  same  formation  as  the  brine  at  Syra- 
cuse and  Warsaw,  N.  Y.  ?  29.  What  uses  are  made  of  the 
Waverly  Sandstone  ?  30.  Mention  localities  where  it  is  quarried. 
31.  What  is  the  character  of  the  Waverly  in  eastern  Pennsyl- 
vania ?  32.  What  underlies  the  Waverly  ?  33.  If  the  Catskill 
Sandstones  should  prove  to  belong  to  the  Waverly  Group,  what 
name  must  we  apply  to  the  Group  ?  34.  What  is  the  position  of 
the  False  Coal  Measures  ? 

XXVII. 

1.  Name  some  towns  where  coal-mining  is  carried  on.  2. 
What  is  the  method  of  mining  when  the  coal  bed  outcrops  ?  3. 
What  is  the  method  when  the  coal  bed  is  deep  beneath  the 
surface  ?  4.  Define  the  terms  drift  and  shaft.  5.  How  is  the 
work  in  a  coal  mine  laid  out  ?  6.  Why  are  two  drifts  or  two 
shafts  necessary  ?  7.  Of  what  kinds  of  rocks  are  the  Coal 
Measures  composed  ?  8.  What  is  the  thickness  of  the  Coal 
Measures  ?  9.  How  many  beds  of  coal  may  there  be  ?  10. 
What  fossils  are  found  in  coal  mines?  11.  How  do  the  strata  of 
the  western  Coal  Measures  differ  from  those  of  Pennsylvania  ? 
12.  What  is  the  cause  of  the  difference?  13.  What  is  a,  fault  in 
geology  ?  14.  What  is  a  downthrow  f  15.  How  extensive  are 
faults  in  some  cases  ?  16.  What  is  the  cause  of  faults  ?  17. 
What  is  the  lowest  stratum  of  the  Coal  Measures  ?  18.  What 
is  sometimes  found  beneath  the  Millstone  Grit  ?  19.  What  for- 
mation in  some  regions  rests  on  the  Coal  Measures  ?  20.  What 
are  the  two  groups  of  the  Upper  Carboniferous?  21.  Enumerate 
now  all  the  groups  of  the  Carboniferous. 


224  GEOLOGICAL   EXCUES1OXS. 

XXVIII. 

1.  What  is  the  geological  position  of  Selma,  Alabama?  2. 
What  systems  of  strata  north  and  south  of  Selma  ?  3.  What  is 
the  "  rotten  limestone  "  ?  4.  Trace  the  Cretaceous  belt  westward 
from  Selma.  5.  Explain  the  numerous  artesian  wells  of  Ala- 
bama. 6.  Explain  the  section,  Figure  72.  7.  What  is  the 
source  of  the  water  in  the  artesian  wells  ?  8.  Why  would  not 
artesian  water  rise  to  the  surface  at  Eutaw  ?  9.  Name  the 
states  which  are  partly  underlaid  by  Cretaceous  strata.  10. 
What  is  the  character  of  the  Cretaceous  rocks  ?  11.  How  do 
they  compare  with  Palaeozoic  rocks  ?  12.  What  formations  in 
Alabama  between  the  Cretaceous  and  the  Coal  Measures  ?  13. 
Explain  this  absence  of  formations.  14.  What  is  meant  by  Jura- 
Trias  ?  15.  Where  do  we  find  the  Jurassic  System  distinctly 
exposed?  16.  What  System  underneath  the  Jurassic?  17. 
Where  is  it  in  America,  and  how  thick  are  the  rocks  ?  18. 
What  formation  in  the  valley  of  the  Connecticut  River  ?  19. 
What  footprints  on  the  layers  of  the  stone  ?  20.  What  use  is 
made  of  this  sandstone?  21.  Mention  other  states  in  which  the 
same  sandstone  occurs.  22.  Now  give  the  names  of  the  three  sys- 
tems embraced  in  the  Mesozoic  Great  System.  23.  Enumerate 
all  the  systems  of  the  Palaeozoic  Great  System.  24.  Enumerate 
all  the  groups  of  the  Palaeozoic  Great  System. 

XXIX. 

1.  In  what  part  of  Alabama  are  the  Tertiary  rocks  ?  2. 
What  of  geological  interest  may  be  seen  at  Claiborne  ?  3.  Of 
what  is  the  Claiborne  bluff  composed  ?  4.  Where  else  may  the 
"  White  Limestone "  be  seen  ?  5.  What  interesting  fossil 
remains  have  been  found  in  it  ?  6.  In  what  three  particulars  do 
the  Tertiary  rocks  differ  from  the  Palaeozoic  ?  7.  To  what 
regions  does  the  Tertiary  extend  ?  8.  What  islands  on  the 
northern  Atlantic  border  are  probably  underlaid  by  Tertiary  ?  9. 
What  sort  of  rocks  is  to  be  seen  at  Gay  Head?  10.  What 
fossils  have  been  found  there  ?  11.  What  great  Tertiary  areas 


QUESTIONS   ON   THE   TEXT.  225 

west  of  the  Mississippi  River  ?  12.  In  what  territories  do  they 
lie  ?  13.  How  do  we  know  that  great  lakes  or  seas  once  rested 
there  ?  14.  Why  have  those  lakes  or  seas  disappeared  ?  15. 
Why  has  the  Atlantic  retreated  from  the  eastern  border  Tertiary  ? 
16.  How  did  the  earlier  and  later  Tertiary  quadrupeds  differ  from 
each  other?  17.  What  was  formed  from  the  sediments  which 
accumulated  in  the  interior  lakes  ?  18.  Where  did  the  sediments 
come  from  ?  19.  What  has  since  happened  to  the  rocks  made 
from  those  sediments  ?  20.  What  is  the  nature  of  our  western 
"  Bad  Lands  "  ?  21.  How  have  their  columnar  forms  come  into 
existence  ? 

XXX. 

1.  Where  may  the  Drift  be  found?  2.  Why  could  not  this 
formation  have  originated  in  a  marine  sediment?  3.  Of  what 
sorts  of  materials  is  the  Drift  composed  ?  4.  In  what  two  par- 
ticulars does  southern  Drift  differ  from  northern  ?  5.  What  is 
the  nature  of  the  lower  portion  of  the  surface  materials  in  the 
Southern  States  ?  6.  In  which  region  is  the  true  transported 
Drift  most  abundant?  7.  What  is  the  character  of  the  rock 
surface  under  the  northern  Drift  ?  8.  In  which  region  do  we  find 
decayed  strata  still  remaining  in  place  ?  9.  In  what  direction  do 
the  grooves  and  scratches  of  the  northern  Drift  extend?  10. 
Mention  localities  where  they  may  be  seen.  11.  Have  you  ever 
seen  any  smoothed  or  striated  rock  surfaces  ?  12.  Do  you  think 
they  exist  in  the  neighborhood  of  your  home  ?  13.  Explain 
what  is  meant  by  "  Modified  Drift."  14.  What  is  "  Till"  ?  15. 
What  is  the  condition  of  the  Drift  around  the  shores  of  the 
Great  Lakes  ?  16.  What  is  a  lacustrine  deposit  ?  17.  What  are 
lake  terraces  ?  18.  How  have  several  river  terraces  been  pro- 
duced along  one  river  ?  19.  What  is  the  proof  of  former  higher 
water  in  our  lakes  and  rivers  ?  20.  How  may  the  water  of  our 
lakes  have  been  dammed  up  ?  21.  What  are  Champlain  deposits  ? 
22.  Enumerate  now,  in  regular  order,  the  surface  materials  of 
the  Northern  States.  23.  Enumerate  the  surface  materials  of 
the  Southern  States.  24.  What  Quaternary  phenomena  exist  at 


226  GEOLOGICAL   EXCURSIONS. 

the  North  and  not  at  the  South  ?      25.  What  exist  at  the  South, 
but  not  at  the  North  ? 

XXXI. 

1.  What  is  the  theory  of  geologists  about  a  former  great 
glacier  in  America?  2.  What  became  of  the  decayed  rock 
material  which  once  covered  the  surface?  3.  How  could  the 
rock-smoothing  and  striation  have  been  produced?  4.  What 
could  have  caused  the  continental  glacier  to  disappear?  5. 
From  what  source  may  we  obtain  light  on  these  questions  ?  6. 
What  is  a  glacier  ?  7.  Does  a  glacier  imply  constant,  extreme 
cold?  8.  Would  a  glacier  exist  in  a  region  where  no  thawing 
ever  took  place  ?  9.  Would  a  glacier  exist  where  but  very  little 
snow  fell?  10.  What  would  you  say  is  requisite  that  a  glacier 
may  come  into  existence  ?  11.  Where  are  the  best  known  glaciers 
of  modern  times  ?  12.  What  is  a  lateral  moraine  ?  13.  What  is 
a  terminal  moraine  ?  14.  Of  what  are  moraines  composed  ?  15. 
What  striking  scene  is  displayed  at  the  foot  of  the  Glacier  des 
Bois  ?  16.  What  is  the  source  of  the  stream  issuing  from  the 
foot  of  a  glacier  ?  17.  Has  the  Glacier  des  Bois  been  increasing 
or  decreasing?  18.  What  are  the  evidences  of  this?  19.  How 
much  has  it  lowered?  20.  How  much  has  it  retreated?  21. 
What  records  of  its  former  action  may  be  seen?  22.  When 
was  the  glacier  close  to  the  village  of  Bois  ?  23.  How  have  the 
boulders  been  strewn  over  the  area  at  present  intervening  ?  24. 
What  do  we  find  in  America  to  remind  us  of  this  moraine  ?  25. 
How  is  it  supposed  the  gravel  ridges  of  America  were  produced? 
26.  How  extensive  must  have  been  the  American  glacier  ?  27. 
What  country  presents  a  real  picture  of  glaciated  America  ? 

XXXII. 

1.  What  does  geology  intimate  respecting  the  age  of  the 
world  ?  2.  What  is  thought  to  have  been  the  earth's  primitive 
condition  ?  3.  How  did  the  ocean  originate  ?  4.  What  was  the 
beginning  of  solid  land  ?  5.  What  were  the  first  living  things  ? 
6.  What  is  the  origin  of  plumbago  ?  7.  Give  some  description 


QUESTIONS    ON   THE   TEXT.  227 

of  the  first  kind  of  animals  ?  8.  In  what  time  did  they  begin  to 
live  ?  9.  What  animals  appeared  in  Palaeozoic  Time  ?  10.  What 
is  a  straight-chambered  shell?  11.  What  changes  were  intro- 
duced with  the  Devonian  Age  ?  12.  What  can  you  say  about 
Lepidodendron  ?  13.  What  can  you  say  about  Pterichthys  f 
14.  What  about  Dinichthys  ?  15.  What  animal  types  dwindled 
away  in  the  Carboniferous  Age  ?  16.  What  was  the  character  of 
the  vegetation  in  the  Carboniferous  Age  ?  17.  How  were  beds 
of  coal  produced  ?  18.  When  were  the  Appalachian  Mountains 
uplifted?  19.  What  can  you  say  about  A  mm  onites  f  20.  How 
did  the  Devonian  fishes  differ  from  modern  fishes?  21.  When 
did  the  modern  types  of  fishes  first  become  abundant?  2$. 
What  were  the  first  air-breathing  vertebrates  ?  23.  What  were 
the  highest  vertebrates  during  Mesozoic  Time?  24.  Mention 
some  of  the  different  kinds  of  reptiles.  25.  Which  of  these 
kinds  no  longer  live  on  the  earth  ?  26.  In  what  respect  were 
some  Mesozoic  birds  reptilian  ?  27.  What  part  of  North  America 
was  under  water  during  the  Mesozoic  ?  28.  How  is  this  shown 
on  the  geological  map  ?  29.  What  change  took  place  in  the 
land  at  the  end  of  the  Mesozoic  ?  30.  What  were  the  highest 
animals  during  the  Tertiary?  31.  What  is  meant  by  compre- 
hensive types  f  32.  What  peculiarities  about  the  brains  of  the 
oldest  mammals  ?  33.  What  about  their  feet  ?  34.  What  was 
the  use  of  the  continental  glacier  to  man  ?  35.  What  was  the 
condition  of  the  people  who  first  inhabited  Europe  ?  36.  How 
have  European  people  become  so  greatly  improved  ?  37.  How 
can  knowledge  make  people  happier? 


Il^DEX. 


This  index  serves  also  as  a  glossary.      The  star  denotes  subjects  illus- 
trated by  cuts. 


Acadian  formation,  139. 

Acid-forming  oxides,  33. 

Acids,  33. 

Actinolite,  51. 

Adirondacks,  113. 

Affinity,  32,  33,  34. 

Ages,  130. 

Alabama,  109,  114,  160,  168,  170, 
171,  173,  174. 

Alabaster,  157. 

Albany,  114. 

Albite,  44. 

Alleghenies,  78.  93*. 

Alluvium,  82. 

Alpena,  144. 

Aluminous,  75. 

Ammonites,  195*. 

Amoeba,  192*. 

Amphibians,  196. 

Animals,  first  advent  of,  191. 

Animals,  fossilized,  191.  See,  also, 
"Fossils." 

Anorthite,  44. 

Appalachians,  78,  92,  93*  109,  111, 
112,  123,  132,  186,  195. 

Archaeopteryx,  198. 

Arched  Rock,  Mackinac,  149*. 

Arctic  Ocean,  197. 

Argillaceous  rocks,  74. 

Argillite,  75. 

Arnot,  Penn.,  162. 

Artesian  wells,  168,  169*. 

Arve,  188. 

Arveyron,  188. 

Asbestus,  51. 

Assortment  of  soil,  20*;  of  sedi- 
ments, 81. 

Atlantic  Ocean,  111,  123. 


Atoms,  31. 
Augite,  51. 

Bad-lands,  177*,  197. 

Bay  View,  150. 

Berea,  Ohio,  157. 

Biotite,  50. 

Birds  of  Mesozoic  Time,  198. 

Biscuit,  76. 

Bivalves,  84,  195. 

Black  Hills,  109. 

Blossburg  mines,  163. 

Bluffs    on    the    Upper    Mississippi, 

132*. 

Bog  iron  ore,  29. 
Bois,  glacier  of,  187,  188*. 
Bossons,  glacier  of,  186,  187*. 
Boston,  114,  115. 
Boulders,  17;  large  examples  of,  17, 

18* ;  where  wanting,  19. 
Boulders  and  sand,  15,  179,  188. 
Boulder-strewn  areas,  19*,  188*,  189. 
Brachiopods,  196. 
Brazil,  Ind.,  160. 
Break,  geological,  136*. 
Bricks,  74,  76. 
Buffalo,  150. 
Burlington,  Iowa,  153. 

Cairo,  111.,  153. 
Calcareous  rocks,'J>9. 
Calciferous,  69. 
Calcite,  34*,  35*. 
Caledonia,  N.  Y.,  150. 
Cambrian  rocks  and  history,  131. 
Cambrian  groups,  135,  139. 
Cambro-Silurian,  113,  114,  122. 
Canada,  111,  113,  127,  144,  150,  180. 


230 


INDEX. 


Carboniferous  limestone,  153. 

Carboniferous  rocks,  153,  160; 
groups,  158,  161. 

Castle  rock,  Minn.,  134*. 

Catskill  group,  158. 

Caves,  origin  of,  94. 

Chalk,  experiment  with,  30;  precip- 
itated, 34;  French,  77. 

Chalk  formation,  170. 

Chalybeate  water,  29. 

Champlain  deposits  and  epoch,  184. 

Charlevoix,  150. 

Charmoz,  needles  of,  126. 

Chemical  elements,  32. 

Chemical  principles,  30. 

Chemung  group,  150. 

Chert,  74. 

Chlorides,  33. 

Chocorua,  Mt.,  126. 

Cincinnati,  114,  132,  138,  139. 

Claiborne,  Ala.,  173. 

Cleavage,  47. 

Cleveland,  157. 

Clinton  formation,  143. 

Club-mosses,  165,  193. 

Coal  Measures,  160. 

Coal  mines,  160,  161;  of  Blossburg 
company,  162. 

Cobble  stones,  15;  mineral  substan- 
ces in,  16. 

Colorado,  92. 

Colorado  River,  90. 

Colors  in  pebbles  and  cobble  stones,  17 

Columbia,  Tenn.,  132. 

Columbus,  Ohio,  151. 

Columns,  geological,  99*,  176,  177*. 

Composition  of  minerals,  53;  of 
rocks,  68. 

Compound  substances,  32. 

Comprehensive  types,  198. 

Conglomerate,  55,  70. 

Connecticut,  19,  45,  55,  71,  113,  171. 

Connecticut  River,  113,  171. 

Corniferous  limestone,  149. 

Cortland,  N.  Y.,  151. 

Crawfordsville,  Ind.,  155. 

Cretaceous  system,  168. 

Crust  of  the  earth,  103. 

Cryptocrystalline,  66. 

Crystalline  form,  42. 

Crystalline  rocks,  77,  96*. 

Cumberland  Mountains,  92;  River, 
114. 


Dakota,  123,  170. 

Dalles  of  the  Wisconsin,  89*. 

Davenport,  Iowa,  153. 

Decay  of  rocks,  87,  91. 

Delaware,  Ohio,  151. 

Delta  of  Mississippi,  86. 

Detroit,  116,  119,  157. 

Devonian  rocks,  146. 

Devonian  groups,  152. 

Diabase,  65. 

Dinichthys,  194*. 

Dinoceras,  198. 

Diorite,  65. 

Dip  of  rocks,  103;  law  of,  108,  109, 
113,  116.  . 

Dog-tooth  spar,  47*. 

Dolomite,  48. 

Downcast  in  a  mine,  161. 

Downs,  25. 

Downthrow,  166. 

Drift,  21,  24,  178;  northern  and 
southern  distinguished,  179,  184; 
modified,  181 ;  connection  of  gla- 
ciers with,  186. 

Drifting  in  a  mine,  160. 

Dunes,  25. 

Effervescence,  34,  69. 

Egyptian  marble,  70. 

Element,  32. 

Elements,  chemical,  32. 

Eozoic  areas  of  U.  S.,  109,  123. 

Eozoic  rocks,  123;  weathering  of, 
125*,  126*;  folding  of,  126*,  127*. 

Eras,  130. 

Erie,  Lake,  145,  151. 

Erosion  of  rocks,  87,  103,  104,  176; 
at  Watkins'  Glen,  88*;  at  Dalles  of 
the  Wisconsin,  89* ;  near  Trempea- 
leau,  90*;  in  Wisconsin,  91*;  in 
Tennessee,  92*;  in  the  Appalachi- 
ans, 93*;  in  Colorado,  92,  94*;  de- 
termining forms  of  mountains,  124, 
125*  ;  of  Cambrian  rocks,  133*, 
134*;  of  general  surface,  137;  at 
Mackinac,  147*. 

Eutaw,  Ala.,  170. 

Falls,  of  Niagara,  140,  141*,  142*; 

of  St.  Anthony,  135. 
False  Coal  Measures,  158.      > 
Face  of  crystal,  42. 


INDEX. 


Faults,  166*. 

Feel  of  a  rock,  52. 

Feldspar,  angles  of,  41*;  crystal  of, 
42 ;  composition  of,  44. 

Feldspars,  40. 

Felsite,  60. 

Ferns  as  fossils,  163. 

Flint,  38. 

Flint  rock,  54. 

Formations,  how  distinguished,  154. 

Folding  of  strata,  126-130*. 

Forces  in  geology,  130. 

Forms  of  mountains,  124,  125*,  126*. 

Fort  Snelling,  134,  135. 

Fossils,  28,  96,  191 ;  distribution  of, 
in  the  rocks,  97,  98;  in  Cambrian 
rocks,  133;  in  Hamilton  rocks,  151, 
in  Coal  Measures,  163,  164*,  165* ; 
in  Tertiary,  175. 

Franklin,  Tenn.,  132. 

Frazer  Bay,  181. 

Gangways,  161. 

Gay  Head,  175. 

Geological  column,  99. 

Georgia,  109. 

fjilsum  boulder,  18. 

Glacial  epoch,  186,  200. 

Glaciers,  185;  in  the  Alps,  186, 187*, 

diminution  of,  189. 
Gloucester  boulder  field,  19. 
Gneiss,  60 ;  syenitic,  65 ;  dioritic,  65 ; 

diabasic,  65. 
Gneissoid,  66. 
Goat  Island,  143. 
Goderich,  144,  150. 
Grand  Haven,  116. 
Grand  Rapids,  157. 
Grand  Traverse  Bay,  118,  149. 
Granite,  59;  porphyritic,  59*;  horn- 

blendic,  64. 
Granulite,  60. 
Granular  quartzite,  55. 
Graphic  slate,  74. 
Gravel  bank,  21,  22,  23*,  26. 
Great  Lakes,  24,  109,  181,  183. 
Greisen,  61. 
Grindstone  City,  157. 
Grit,  55. 
Gypsum,  where  found,  157. 

Hamilton  group,  149. 


Hammers,  36*. 

Hard  water,  28. 

Hardness-tester,  37*. 

Helderberg  group,  145. 

Hexagonal  prism,  38. 

Hornblende,  50,  51*. 

Hornblende,  schist,  65;  rock,  65. 

Hornblendic  rocks,  62. 

Hornets'  Nest,  Wis.,  133*. 

Hudson  River,  145,  172. 

Huron  grindstones,  157. 

Huron,  Lake,  111,  144, 146, 148,  157, 

180,  189. 

Huronian  system,  99,  109,  128. 
Hydromica,  51. 
Hyposyenite,  65. 

Identifications,  exercises  in,  78. 

Illinois,  64,  145,  160,  163,  165. 

Indiana,  25,  64,  145,  152. 

Indian  Territory,  124. 

Indurated  and  semi-indurated,  77. 

Ingersoll,  Ont.,  150. 

Inorganic,  14. 

Invertebrate,  97. 

Iowa,  56,  170. 

Iron  ores,  where  found,  128. 

Iron  range,  section  through,  129*. 

Iron  rust,  33. 

Ithaca,  N.  Y.,  151. 

Jasper,  38. 

Jurassic,  109,  113,  114,  171. 

Jura-Trias,  171. 

Kansas,  112,  160,  170,  171. 
Kaolin,  45,  76. 

Kearsarge,  ML,  125*,  126*,  127, 130. 
Kentucky  19,  111,  132,  155,  156,  160, 

160,  167. 

Kewenian  rocks,  129*. 
Knobs,  156. 

Labradorite,  44. 

Lacustrine  deposits,  182. 

Lake  barriers,  183. 

Lakelet  filling,  83*. 

Lake  terraces,  182. 

Lamellae,  43. 

Laminae,  22,  96. 

LaSalle,  111.,  160. 

Laurentian  system,  99, 109,  128, 129. 


232 


INDEX. 


Lebanon,  132. 

Lepidodendron,  165*,  193. 

Lewiston,  142. 

Lexington,  Ky.,  132. 

Lime,  72. 

Limestone,  71 ;  oolitic,  72 ;  varieties 

of,  72,  78. 

Limewater,  experiment  with,  30. 
Little  Traverse  Bay,  118,  149. 
London,  Ont.,  150. 
Louisiana,  174. 
Lustre,  glassy,  38,  43,  48 ;  pearly,  41, 

43. 

Mac  Gregor,  Iowa,  135. 

Mackinac,  118,  146,  147,  148. 

Madison,  Ind.,  132. 

Magnesian  limestone  formation,  135. 

Magnesite,  48. 

Magnifying  glasses,  43. 

Maine,  64,  123,  145. 

Mammals,  197;  in  the  Tertiary  Age, 

197,    198*;    in  the  Post  Tertiary, 

199*. 

Mammoth  Cave,  155. 
Man  in  geology,  200. 
Manitoulin  Islands,  131. 
Map  constructed  from  a  section,  105*, 

106*. 
Map,  geological,  explained,  109, 110*; 

exercises  on,  113,  114,  115. 
Marbles,  69;  saccharoidal,  70;  statu- 
ary, 70;   argillaceous  veinings  in, 

70 ;  where  found,  128. 
Margarodite,  51. 
Marl,  28,  72. 

Marquette  iron  region,  128, 181,  188*. 
Marsh,  how  formed,  82*,  84. 
Martha's  Vineyard,  24,  29,  174. 
Maryland,  71,  109. 
Massachusetts,  19,  45, 64,  71, 113, 114, 

123,  132,  139,  145. 
Medina  sandstone,  144. 
Megatherium,  199. 
Merde  Glace,  187. 
Mesozoic  rocks,  168;  systems,  172. 
Metamorphism,  97,  113. 
Mexican  gulf,  86,  168,  171,  197. 
Micaceous  rocks,  57. 
Micas,  50. 
Mica-schist,  61. 
Michigan,  17,  18,  23,  56,  64,  71,  112, 

113,  116,  118,  119,  129,  131,  146, 

155,  156. 


Michigan,  Lake,  112,  117,  118,  146, 

148. 

Millstone  grit,  167. 
Milwaukee,  113,  119. 
Mineral,  14,  16. 
Minerals,  composition  of,  53. 
Minneapolis,  35. 
Minnehaha  Falls,  135. 
Minnesota,  64,  78,  90,  131,  134,  137, 

170. 
Mississippi  Eiver,  85,  86,  90,  133, 135, 

153. 
Missouri,  19,  112,  123,  128.  145,  151, 

160. 

Missouri  River,  85,  95. 
Mobile,  114,  169. 
Modified  Drift,  181. 
Montana,  171. 
Mont  Blanc,  186,  188. 
Monument  Park,  Colorado,  94*. 
Moraines,  187*,  188*. 
Moss,  "petrified, "28* 

Nantucket,  174. 

Nashville,  114,  122,  132. 

Nebraska,  170. 

New  Brunswick,  145,  157. 

New  England,  19,   71,  77,  96,  113, 

180. 
New  Hampshire,  17,  50, 123, 127,  131, 

145. 

New  Haven,  172. 
New  Jersey,  55,  96,  172,  174. 
New  Mexico,  177. 
New  York,  28,  48,  55,  71,  78,  88,  89, 

113,  123,  132,  140,  144,  151,  158. 
Niagara  Falls  and  gorge,  140,  141*, 

142*. 
Niagara  limestone,  142;   shale,  143; 

group,  145. 

North  Carolina,  64,  109,  172. 
Nova  Scotia,  139,  145. 

Ochre,  29. 

Ohio,  55,  64,  111,  114,  132,  145,  151, 

155,  160. 
Ohio  River,  151,  155,  157,  169,  186, 

194. 

Oneida  conglomerate,  144. 
Ontario,   Lake,   111,   113,    120,   121, 

132,  141. 
Oolitic  limestones,  154. 


INDEX. 


233 


Organic  and  inorganic,  13. 

Organic  products,  14. 

Organs,  13. 

Oriskany  sandstone,  150. 

Orthoceras,  193;  restoration  of ,  193*. 

Orthoclase,  42*,  44. 

Outcrop  of  strata,  103. 

Outliers   of    Cambrian   rocks,    134*, 

137. 

Overlying  formations,  103. 
Oxides,  32,  33. 

Panama,  N.  Y.,  151. 

Parian  marble,  76. 

Peat,  82 ;  formation  of,  83*. 

Pebbles,  15,  16;  colors  and  grains  in, 

16. 
Pennsylvania,  55,  93,  111,  120,  156, 

158,  166. 

Penokie  range,  128,  129. 
Permian  group,  167. 
Petoskey,  150. 
Petrosilex,  60. 
Phanerocrystalline,  66. 
Pilot  Knob,  128. 
Plagioclase,  44. 

Plants  in  the  rocks,   163,  164*,  165*. 
Porcelain,  45,  76. 
Porphyritic,  59. 
Portland,  Conn.,  171. 
Post  Tertiary,  109. 
Potomac  marble,  70. 
Potsdam  sandstone,  135,  137,  139. 
Pottery,  76. 
Prairie  du  Chien,  133. 
Profile,  geological,  119. 
Protogine,  66. 
Pterichthys,  194*. 
Pudding  stone,  70. 

Quartz,  36,  37,  39*. 
Quartzite,  54 ;  striated  dome  of,  180*. 
Quartzose  rocks,  54. 
Quaternary  formations,  178;    classi- 
fied, 184. 
Quebec,  145. 

Questions  on  the  Text,  202. 
Quincy  granite,  64. 

Recession  of  Niagara  Falls,  143. 
Reptiles,  196*;  bipedal,  197*. 
Rhode  Island,  113,  123. 


Richmond,  Ind.,  132. 
Rock  salt,  144. 
Rocky  Mts.,  95. 
Rotten  limestone,  168. 

Saginaw  Bay,  157. 

Salina  group,  144. 

Salt  in  Salina  group,  144;  in  Car- 
boniferous limestone  group,  157. 

Salt  wells,  144,  145. 

Salts;  33. 

Sandstone,  55 ;  varieties  of,  78. 

Sandusky,  114,  151. 

Savannah,  122. 

Scenery  of  Chemung  rocks,  151. 

Schist,  mica,  61;  hydromica,  61; 
hornblende,  65;  talcose,  66. 

Schistose,  66. 

Scotch  granite,  64. 

Section  constructed  from  a  map,  106*, 
116,  117-122*. 

Section  of  the  earth's  crust,  107*. 

Section  from  Detroit  to  Grand  Haven, 
116-119*;  from  Canada  to  Will- 
iamsport,  120-121*;  from  Nash- 
ville to  Savannah,  122*;  through 
Mt.  Kearsarge,  126*,  130;  in  Can- 
ada, 127*;  in  Wisconsin,  128*; 
through  an  iron  range,  129* ;  along 
the  Upper  Mississippi,  135* ;  across 
the  Cincinnati  swell,  139*;  across 
Mackinac  Island,  147*;  at  Burling- 
ton, Iowa,  153* ;  in  Coal  Measures 
of  111.,  165*;  in  Coal  Measures  of 
Penn.,  166*;  in  Alabama,  169*. 

Sediments,  81,  85,  86. 

Selma,  Ala.,  168,  169,  170. 

Septa  of  chambered  shells,  195. 

Soapstone,  52,  66. 

Soft  water.  29. 

Soil,  what  composed  of,  20. 

Solution,  27. 

South  Carolina,  109. 

Springs  and  wells,  26*. 

Stalactite,  72. 

Stalagmite,  72. 

St.  Anthony  Falls,  135. 

Steatite,  52,  66. 

St.  Ignace  boulders,  18. 

St.  Lawrence  River,  109,  111,113; 
Gulf,  151. 

Stone  lilies,  154,  155. 


234 


INDEX. 


St.  Paul,  Minn.,  133,  134,  135. 

St.  Peter's  sandstone,  135,  137. 

Strata,  24,  85,  96;  systems  of,  95; 
enwrapping  the  earth,  101,  102*; 
folding  of,  126-130*;  of  Coal 
Measures,  163,  165*,  166*. 

Stratification,  22,  59. 

Strise  on  feldspars,  43. 

Striated  rock-surfaces,  180*. 

Structure,  below  the  surface,  import- 
ant, 112,  116;  of  Mt.  Kearsarge, 
126*. 

St.  Stephens,  Ala,  169,  174. 

Sugar  loaf,  Mackinac,  148*. 

Superposition  of  rocks,  rule  of,  97,98. 

Switzerland,  125,  185. 

Syenite,  63;  micaceous,  64. 

Syracuse,  N.  Y.,  150. 

Systems  of  strata,  95,  98,  99*,  102*. 

Table  of,  samples  of  rocks  and  min- 
erals, 11 ;  elements,  32 ;  composition 
of  minerals,  53;  composition  of 
rocks,  68;  fragmental  rocks,  77; 
for  rock-determination,  79;  geo- 
logical formations,  99*;  quater- 
nary formations,  184. 

Table-rock,  141*,  143. 

Taconnay,  glacier  of,  186,  187* 

Talc,  50,  52. 

Talcose,  66. 

Talus.  22. 

Tennessee,  70,  91,  92,  111,  114,  160, 
167. 

Tennessee,  great  erosion  in,  92*. 

Terminations  of  crystals,  39*. 

Terrace  formation,  184. 

Terraces,  182. 

Terrible  fish,  194*. 

Tertiary  formations,  173. 

Tertiary  lakes  or  seas,  176. 


Texas,  112,  170,  171,  174. 
j   Theory,  specimen  of,  147. 
Till,  181. 
Toledo,  157. 

Tombigbee  River,  169,  174. 
Tourmaline,  56. 
Travertin,  28,  72. 
Tremolite,  51. 
Trempealeau,  cliffs  at,  90*. 
Triassic  system,  171. 
Trilobites,  192. 
Tufa,  28*,  72. 
Tuscaloosa,  169. 

Unaka  Range,  91. 
Unconformability,  136*. 
Univalves,  84. 
Utah,  166. 

Vein,  40,  42,  57. 
Vermont,  17,  70,  71,  131,  139. 
Virginia,  19,  109,  158,  172. 
Vitreous  quartzite,  55. 

Warsaw,  N.  Y.,  145. 
Washington,  Mt.,  124,  127. 
Watkins'  Glen,  88*. 
Waverly  group,  154;  sandstone,  157. 
Weathering  of  rocks,  124;  see   also 

"Erosion." 
Western  states,  28. 
White  limestone  in  Ala.,  173. 
White  Mountains,  124,  130. 
Wilkesbarre,  160. 
Williamsport,  Penn.,  120. 
Winged  fish,  194*. 
Wisconsin,  64,  89,  90,  91,  111,  112, 

113,  119,  123,  128,  131,  134,  136r 

137. 

Wyandotte  cave,  156. 
Wyoming,  145. 


YC  49599 


5^*1810 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


